演算法與資料結構（Algorithms and Data structures）

• Algorithmia - Algorithm and data-structure library for .NET 3.5 and up. Algorithmia contains sophisticated algorithms and data-structures like graphs, priority queues, command, undo-redo and more.
• C# Algorithms - A C# plug-and-play class-library project of standard Data Structures and Algorithms. It contains 35+ Data Structures and 30+ Algorithms designed as Object-Oriented isolated components.

應用程式介面（API）

• NancyFx - Lightweight, low-ceremony, framework for building HTTP based services on .Net and Mono
• ASP.NET WebAPI - Framework that makes it easy to build HTTP services that reach a broad range of clients, including browsers and mobile devices
• Breeze - Api framework enabling rich data access by using the OData 3 protocol. Client libraries available for Javascript and C#.
• Mobius: C# API for Spark - Mobius adds C# language binding to Apache Spark, enabling the implementation of Spark driver code and data processing operations in C#.
• ServiceStack - Thoughtfully architected, obscenely fast, thoroughly enjoyable web services for all
• Nelibur - Nelibur is message based web service framework on the pure WCF. Nelibur simplifies creating high-performance and message based web services and you certainly have all the power of the WCF.
• WebAPI Contrib - Collection of open source projects to help improve your work with ASP.NET Web API

應用程式框架（Application Frameworks）

• ASP.NET Boilerplate - A starting point for new modern ASP.NET MVC web applications with best practices and most popular tools.
• Orleans - Orleans is a framework that provides a straight-forward approach to building distributed high-scale computing applications, without the need to learn and apply complex concurrency or other scaling patterns
• CoreFX - The corefx repo contains the library implementation (called "CoreFX") for .NET Core. It includes System.Collections, System.IO, System.Xml and many other components. It builds and runs on Windows. You can 'watch' the repo to see Linux and Mac support being added over the next few months.
• Mono - Mono open source ECMA CLI, C# and .NET implementation
• Mono-Addins - Mono.Addins is a generic framework for creating extensible applications, and for creating add-ins which extend those applications
• peasy - Peasy is a middle tier framework that offers an easy to use and flexible rules engine and was designed to address common challenges such as concurrency handling, transactional support, fault tolerance, threading, scalability, async and multiple client support, and easy testability, all without a huge learning curve!
• Spring.Net - Spring.NET is an open source application framework that makes building enterprise .NET applications easier
• DotNetty - DotNetty is a port of Netty, asynchronous event-driven network application framework for rapid development of maintainable high performance protocol servers & clients.

模板引擎（Application Templates）

• ASP.NET Core Starter Kit - backend: .NET Core, EF Core, C#; frontend: Babel, Webpack, React, CSS Modules
• MVC.Template - ASP.NET Core MVC project starter template.
• ProjectScaffold - A prototypical .NET solution recommended by the F# Foundation---includes file system setup, Paket for dependencies and FAKE for build/test automation. By default, build process also compiles documentation and generates NuGet packages.
• Serene - Serenity is an ASP.NET MVC application platform designed to simplify and shorten development of data-centric business applications with a service based architecture. Serene is a starter template to build Serenity applications.
• Side-Waffle - Large collection of useful templates for Web and Desktop development.
• Template10 - Windows 10 templates with design patterns.

人工智慧（Artificial Intelligence）

• AIMLBot (Program#) - A small, fast, standards-compliant yet easily customizable implementation of an AIML (Artificial Intelligence Markup Language) based chatter bot in C#.
• SIML - Synthetic Intelligence Markup Language, a next generation Chatbot & Digital Assistant Language.

程式集與裝配件（Assembly Manipulation）

• dnSpy - dnSpy is a .NET assembly editor, decompiler, and debugger forked from ILSpy.
• Fody - Extensible tool for weaving .net assemblies
• Mono.Cecil - Cecil is a library to generate and inspect programs and libraries in the ECMA CIL form.

資源（Assets）

• Cassette - Manages .NET web application assets (scripts, css and templates)
• NodeAssets - Asset Manager for .net that has live css updates using SignalR and can optionally leverage NodeJS compilers
• Bundle Transformer - Modular extension for Microsoft ASP.NET Web Optimization Framework. Its modules supports LESS, Sass, CoffeeScript, TypeScript, Mustache, Handlebars, Autoprefixer along with a bunch of different JS and CSS minifiers.
• Bundler - Compile & Minify Less/Sass/Stylus/Css/JS/CoffeeScript/LiveScript files. Integrates with MVC and ServiceStack
• SquishIt - Lets you easily bundle some css and javascript

驗證與授權（Authentication and Authorization）

• ASP.NET Identity - New membership system for ASP.NET applications
• DotNetOpenAuth - A C# implementation of the OpenID, OAuth and InfoCard protocols
• Logibit Hawk - A F# Hawk authentication library
• IdentityModel - Helper library for identity & access control in .NET 4.5 and MVC4/Web API.
• IdentityServer - Extensible OAuth2 and OpenID Connect provider framework.
• OAuth - A very lightweight library for generating OAuth 1.0a signatures written in C#
• Stuntman - Stuntman is a library for impersonating users during development leveraging .NET Claims Identity.

Books

• .NET Core in Action - teaches how to write applications and libraries with .NET Core. [$]
• CLR via C# - Dig deep and master the intricacies of the common language runtime, C#, and .NET development. [$]
• Functional Programming in C# - teaches how to best leverage the functional features of the C# language. [$]
• Microservices in .NET Core - shows you how to build maintainable, secure and operations-friendly microservices using Nancy and .NET Core. [$]

Build Automation

• Psake - .NET-based build automation tool written in PowerShell
• FAKE - F# Make, a cross platform build automation system
• Invoke-Build - PowerShell build and test automation tool inspired by Psake.
• MSBuild - The Microsoft Build Engine (MSBuild) is the build platform for .NET and Visual Studio
• Cake - Cake (C# Make) is a cross platform build automation system with a C# DSL.
• Nake - Magic script-based C# task runner

Caching

• CacheCow - An ASP.NET Web API HTTP caching implementation both on client and server
• Akavache - An asynchronous, persistent key-value store
• CacheManager - A common interface and abstraction layer for caching.
• CacheAdapter - Another common cache abstraction layer for caching with enhanced cache API usage.
• Foundatio - A common interface with in memory, redis and hybrid implementations.

CLI

• Command Line Parser - The Command Line Parser Library offers to CLR applications a clean and concise API for manipulating command line arguments and related tasks
• Fluent Command Line Parser - A simple, strongly typed .NET C# command line parser library using a fluent easy to use interface
• Power Args - PowerArgs converts command line arguments into .NET objects that are easy to program against. It also provides a ton of optional capabilities such as argument validation, auto generated usage, tab completion, and plenty of extensibility
• Argu - Declarative CLI argument & XML configuration parser for F# applications.
• Appccelerate - Command Line Parser - A command line parser with fluent definition syntax, different argument types, required and optional arguments, value restrictions, aliases, type conversion and semi-automatic usage help message composition

CLR

• CoreCLR - The coreclr repo contains the complete runtime implementation (called "CoreCLR") for .NET Core. It includes RyuJIT, the .NET GC, native interop and many other components. It builds and runs on Windows. You can 'watch' the repo to see Linux and Mac support being added over the next few months.

CMS

• Composite C1 - A web CMS that focus on UX and adaptability
• mojoPortal - MojoPortal is an extensible, cross database, mobile friendly, web content management system (CMS) and web application framework written in C# ASP.NET
• N2CMS - Open source, lightweight, code-first CMS able to seamlessly integrate into any MVC project.
• Orchard - Free, open source, community-focused project aimed at delivering applications and reusable components on the ASP.NET platform
• Piranha CMS - Piranha is the fun, fast and lightweight .NET framework for developing cms-based web applications with an extra bite. It's built on ASP.NET MVC and Web Pages and is fully compatible with both Visual Studio and WebMatrix. http://piranhacms.org
• Umbraco - Umbraco is a free open source Content Management System built on the ASP.NET platform
• BetterCMS - Open Source .NET Intuitive User Interface for Developer and Publisher
• DotNetNuke - DNN Platform is our free, open source web CMS and the foundation of every professional DNN solution. Over 750,000 organizations worldwide have built websites powered by the DNN Platform.

Code Analysis and Metrics

• App.Metrics - App Metrics is an open-source and cross-platform .NET library used to record and report metrics within an application and reports it's health. See the docs for me details.
• CodeMaid - Visual studio extension to cleanup, dig through and simplify C#, C++, F#, VB, PHP, JSON, XAML, XML, ASP, HTML, CSS, LESS, SCSS, JavaScript and TypeScript coding.
• StyleCop - StyleCop analyzes C# source code to enforce a set of style and consistency rules
• Gendarme - Extensible rule-based tool to find problems in .NET applications and libraries
• Metrics-Net - Capturing CLR and application-level metrics. So you know what's going on.
• AspNet.Metrics - Capturing CLR, application-level web request metrics. Middleware and extensions using Metrics-Net
• BenchmarkDotNet - Powerful .NET library for benchmarking.
• Codinion - Enhanced syntax highlighting for C# and some other "Visual" features.

Code Snippets

• .NET Fiddle - Write, compile and run C# code in the browser. The C# equivalent of JSFiddle.
• Gistlyn - Create, run and share your executable C# Github Gists.
• TryRoslyn - Run C# code using different branches and versions of Roslyn.

Compilers, Transpilers and Languages

• ClojureCLR - A port of Clojure to the CLR, part of the Clojure project
• F# - The F# compiler, core library and tools - a functional programming language for safer, faster, better code writing.
• FunScript - F# to JavaScript compiler with JQuery etc. mappings through a TypeScript type provider.
• IronScheme - R6RS Scheme compiler, runtime and many standard libraries
• JSIL - CIL to Javascript Compiler http://jsil.org/
• Mono-basic - Visual Basic Compiler and Runtime
• Nemerle - Nemerle is a high-level statically-typed programming language for the .NET platform. It offers functional, object-oriented and imperative features. It has a simple C#-like syntax and a powerful meta-programming system. http://nemerle.org/About
• Netjs - .NET to TypeScript and JavaScript compiler. Portable Class Libraries work great for this. You can even pass EXEs.
• P - P is a language for asynchronous event-driven programming.
• Roslyn - The .NET Compiler Platform ("Roslyn") provides open-source C# and Visual Basic compilers with rich code analysis APIs. It enables building code analysis tools with the same APIs that are used by Visual Studio.
• VisualFSharp - The Visual F# compiler and tools
• Fable - F# to JavaScript Compiler
• LinqOptimizer - An automatic query optimizer-compiler for Sequential and Parallel LINQ
• Roslyn-linq-rewrite - Compiles C# code by first rewriting the syntax trees of LINQ expressions using plain procedural code, minimizing allocations and dynamic dispatch.

Compression

• SharpCompress - SharpCompress is a compression library for .NET/Mono/Silverlight/WP7 that can unrar, un7zip, unzip, untar unbzip2 and ungzip with forward-only reading and file random access APIs. Write support for zip/tar/bzip2/gzip are implemented
• DotNetZip.Semverd - An open-source project that delivers a .NET library for handling ZIP files, and some associated tools. (fork of Unmaintained DotNetZip)
• SharpZipLib - a Zip, GZip, Tar and BZip2 library written entirely in C# for the .NET platform
• Snappy for Windows - Snappy compression library for .NET baked on PInvoke
• Snappy.Sharp - An implementation of Google's Snappy compression algorithm in C#.

Continuous Integration

• TeamCity - Ready to work, extensible and developer-friendly build server — out of the box [$]
• CruiseControl.NET - an Automated Continuous Integration server, implemented using the .NET Framework
• MyGet - Continuous Integration and Deployment, Hosted Package Repository for NuGet, NPM, Bower and VSIX. [$]
• AppVeyor - .NET Continuous Integration and Deployment as a service. [$] [Free for OSS]

Cryptography

• BouncyCastle - Together with the .Net System.Security.Cryptography, the reference implementation for cryptographic algorithms on the CLR.
• HashLib - HashLib is a collection of nearly all hash algorithms you've ever seen, it supports almost everything and is very easy to use
• libsodium-net - libsodium for .NET - A secure cryptographic library
• Pkcs11Interop - Managed .NET wrapper for unmanaged PKCS#11 libraries that provide access to the cryptographic hardware
• StreamCryptor - Stream encryption & decryption with libsodium and protobuf

Database

• BrightstarDb - BrightstarDB is a native .NET RDF triple store
• Event Store - The open-source, functional database with Complex Event Processing in JavaScript. https://geteventstore.com
• LiteDB - A .NET NoSQL Document Store in a single data file - http://www.litedb.org
• RavenDB - A linq enabled document database for .NET
• Marten - Postgresql as a Document Database and Event Store for .Net Applications
• Streamstone - Event store for Azure Table Storage
• Ignite - Distributed in-memory platform: document database with SQL and LINQ support; distributed computations; distributed services and events.
• Yessql - A .NET document database working on any RDBMS

Database Drivers

• MySQL Connector - Connector/Net is a fully-managed ADO.NET driver for MySQL
• Npgsql - .Net data provider for Postgresql
• MongoDB - Official MongoDB C# Driver
• RethinkDb.Driver - A RethinkDB database driver in C# striving for 100% ReQL API compatibility and completeness.
• ServiceStack Redis - .NET's leading C# Redis Client
• StackExchange Redis - General purpose redis client from StackExchange
• Cassandra - DataStax .NET Driver for Apache Cassandra
• Couchbase - Official couchbase .NET client library, based on the Enyim memcached client
• Firebird.NET - The .NET Data provider is written in C# and provides a high-performance, native implementation of the Firebird API

Datetime

• NodaTime - Noda Time is an alternative date and time API for .NET. It helps you to think about your data more clearly, and express operations on that data more precisely. http://nodatime.org/
• DateTimeExtensions - Common Date Time operations on the form of extensions to System.DateTime, including holidays and working days calculations on several culture locales.
• Exceptionless.DateTimeExtensions - DateTimeRange, Business Day and various DateTime, DateTimeOffset, TimeSpan extension methods.

Decompilation

• ILSpy - ILSpy is the open-source .NET assembly browser and decompiler

Deployment

• Unfold - Powershell-based deployment solution for .net web applications
• DbUp - .NET library that helps you to deploy changes to SQL Server databases. It tracks which SQL scripts have been run already, and runs the change scripts that are needed to get your database up to date
• Octo Pack - Used to build nuget packages of your application for deployment using tools such as Octopus Deploy

DirectX

• SlimDX - DirectX framework wrapper for .NET applications
• SharpDX - SharpDX is an open-source project delivering the full DirectX API for .Net on all Windows platforms, allowing the development of high performance game, 2D and 3D graphics rendering as well as realtime sound application.

Distributed Computing

• Orleans - Orleans is a framework that provides a straight-forward approach to building distributed high-scale computing applications, without the need to learn and apply complex concurrency or other scaling patterns. It was created by Microsoft Research.
• Orleankka - Orleankka is a functional API for Microsoft Orleans framework. It is highly suitable for scenarios where having composable, uniform communication interface is preferable, such as: CQRS, event-sourcing, re-routing, FSM, etc. Additional API avaiable for F# called Orleankka.FSharp.
• Akka.net - Akka.NET is a port of the popular Java/Scala framework Akka to .NET. This is a community driven port and is not affiliated with Typesafe who makes the original Java/Scala version.
• Zebus - Zebus is a lightweight, higlhy versatile, peer to peer service bus, built with CQRS principles in mind. It allows applications to communicate with each other in a fast and easy manner. Most of the complexity is hidden in the library and you can focus on writing code that matters to you, not debugging messaging code. A very fundamental base for any distributed application.
• FsShelter - F# library for authoring Apache Storm components and topologies. Offering high-level abstractions for distributed and fault-tolerant event stream processing.
• Foundatio - Pluggable foundation blocks for building distributed apps.
• MBrace - Integrated Data Scripting for the Cloud

DLR

• cmd - C# library to run external programs in a simpler way. Demonstration of "dynamic" features of C#.

Documentation

• Sandcastle - Sandcastle Help File Builder similar to NDoc
• SharpDox - A c# documentation tool
• Swashbuckle - Seamlessly adds a swagger to WebApi projects!
• F# Formatting - Tools for documenting F# and C# projects from F# Script files, Markdown documents and inline XML or Markdown comments
• DocFX - Tools for building and publishing API documentation for .NET projects
• DocNet - Your friendly static documentation generator, using markdown files to build the content.

Exceptions

• Exceptionless - Exceptionless .NET Client

E-Commerce and Payments

• Paypal Merchant SDK - Official Paypal Merchant SDK for .NET
• NopCommerce - nopCommerce. Free open-source ecommerce shopping cart (ASP.NET MVC)
• ServiceStack.Stripe - Typed .NET clients for stripe.com REST APIs
• Virto Commerce - Virto Commerce is the second generation release and is the only enterprise level e-commerce product fully available under Open Source license. Virto Commerce is based on .NET 4.5 with extensive use of MVC, IoC, EF, Azure, Angular JS and many other cutting edge technologies. It can be deployed in Microsoft Cloud (Azure), Amazon Web Services (AWS) and on-premise. https://virtocommerce.com

Environment Management

• Dotnet CLI - The cross-platform .NET Core command line toolchain utility.

ETL

• Reactive ETL - Reactive ETL is a rewrite of Rhino ETL using the reactive extensions for .NET

Functional programming

• language-ext - This library uses and abuses the features of C# 6+ to provide a functional 'Base class library', that, if you squint, can look like extensions to the language itself. It also includes an 'Erlang like' process system (actors) that can optionally persist messages and state to Redis (note you can use it without Redis for in-app messaging). The process system additionally supports Rx streams of messages and state allowing for a complete system of reactive events and message dispatch.

Game

• MonoGame - One framework for creating powerful cross-platform games
• CocosSharp - CocosSharp is a C# implementation of the Cocos2D and Cocos3D APIs that runs on any platform where MonoGame runs
• Duality - Duality is a 2D game development framework. Focused on modularity, comes with a visual editor.
• Xenko - Xenko is a 2D/3D cross-platform game engine featuring a scene editor, particles, physically based rendering (PBR), scripting, and much more
• Wave Engine - Wave engine is a free c# component-based modern game engine which allows you to create cross-platform games supporting kinect, oculusrift, vuforia, cardboard, leapmotion and much more. [Free][Proprietary]
• UrhoSharp - UrhoSharp is a C# implementation of the Urho3D game engine that runs on iOS, Mac, Windows, Android and Linux systems
• Nez - Nez is a free 2D focused framework that works with MonoGame and FNA

GIS

• NetTopologySuite A .NET GIS solution that is fast and reliable for the .NET platform
• SharpMap An easy-to-use mapping library for use in web and desktop applications
• OsmSharp - C# library to work with OpenStreetMap (OSM) data. Provides reading, writing and route-planning for OSM data.

Git Tools

• Bonobo Git Server - Bonobo Git Server for Windows is a web application you can install on your IIS and easily manage and connect to your git repositories. https://bonobogitserver.com/
• GitExtensions - GitExtensions is a shell extension, a Visual Studio 2008/2010/2012/2013 plugin and a standalone Git repository tool. http://gitextensions.github.io/
• GitLink - let's users step through their code hosted on GitHub or BitBucket
• GitVersion - Generate a Semantic Version Number based on the state of your Git Repository
• LibGit2Sharp - LibGit2Sharp brings all the might and speed of libgit2, a native Git implementation, to the managed world of .Net and Mono.
• NGit - NGit is a port of JGit to C#
• posh-git - A PowerShell environment for Git
• Git Credential Manager for Windows - Helps solving issues of credentials, made by Microsoft

Graphics

• LibTessDotNet - .NET port of the famous GLU Tessellator, triangulates polygons
• Oxyplot - OxyPlot is a cross-platform plotting library for .NET
• OpenTK - The Open Toolkit is an advanced, low-level C# library that wraps OpenGL, OpenCL and OpenAL
• NGraphics - NGraphics is a cross-platform library for rendering vector graphics on .NET
• Live-Charts - An Animated, MVVM oriented and modern charting library

GUI

• MahApps.Metro - Toolkit for creating Metro styled WPF apps
• Callisto - A control toolkit for Windows 8 XAML applications. Contains some UI controls to make it easier to create Windows UI style apps for the Windows Store in accordance with Windows UI guidelines.
• ObjectListView - ObjectListView is a C# wrapper around a .NET ListView. It makes the ListView much easier to use and teaches it some new tricks
• DockPanelSuite - The Visual Studio inspired docking library for .NET WinForms
• AvalonEdit - The WPF-based text editor component used in SharpDevelop
• XWT - A cross-platform UI toolkit for creating desktop applications with .NET and Mono
• Gtk# - Gtk# is a Mono/.NET binding to the cross platform Gtk+ GUI toolkit and the foundation of most GUI apps built with Mono
• Eto.Forms - Cross platform GUI framework for desktop and mobile applications in .NET and Mono
• Dragablz - Dragable, tearable WPF tab control (similar to Chrome) which supports layouts and is full themeable, including themese compatible with MahApps and Material Design.
• Fluent.Ribbon - Fluent Ribbon Control Suite is a library that implements an Office- and Windows 8-like Ribbon for WPF.
• Office Ribbon - A library that implements MS Office Ribbon for WinForms.
• Perspex - A multi-platform .NET UI framework.
• MaterialSkin - Theming .NET WinForms, C# or VB.Net, to Google's Material Design Principles.
• Xamarin.Forms - Build native UIs for iOS, Android and Windows from a single, shared C# codebase.
• SciterSharp - Create .NET cross-platform desktop apps using not just HTML, but all features of Sciter engine: CSS3, SVG, scripting, AJAX, <video>... Sciter is free for commercial use
• Empty Keys UI - Multi-platform and multi-engine XAML based user interface library [Free][Proprietary]
• UWP Community Toolkit - The UWP Community Toolkit is a collection of helper functions, custom controls, and app services. It simplifies and demonstrates common developer tasks building UWP apps for Windows 10.
• ScintillaNET - Windows Forms control for the Scintilla text editor component (Scintilla is used by Notepad++)
• FastColoredTextBox - Fast Colored TextBox is text editor component for .NET. Allows you to create custom text editor with syntax highlighting. It works well with small, medium, large and very-very large files.

HTML and CSS

• AngleSharp - Complete HTML5 DOM and CSS3 OM construction
• CsQuery - HTML5 parser with jQuery style DOM interaction
• ExCSS - CSS3 parser Library for C#
• FluentBootstrap - Makes the Bootstrap CSS framework easier to use from ASP.NET MVC or WebPages.
• HtmlAgilityPack - an agile HTML parser that builds a read/write DOM and supports plain XPATH or XSLT

HTTP

• Http.fs - A functional HTTP client for [F#].
• RestSharp - Simple REST and HTTP API Client for .NET
• Flurl.Http - Fluent, portable, testable REST/HTTP client library
• EasyHttp - Http Library for C#
• Refit - The automatic type-safe REST library for Xamarin and .NET
• RestEase - Easy-to-use typesafe REST API client library, which is simple and customisable. Heavily inspired by Refit
• HttpClientGoodies - utilities for working with HttpClient

IDE

• SharpDevelop - A free IDE for .NET programming languages
• MonoDevelop - MonoDevelop is a cross platform IDE mostly aimed at Mono/.NET developers
• Visual Studio Express - The free lightweight version of Visual Studio for .NET programming.
• Waf DotNetPad - A simple and fast code editor that makes fun program with C# or Visual Basic.
• Visual Studio Code - Excellent free editor from Microsoft, based on GitHub Atom.
• Ionide - An Atom Editor and Visual Studio Code package suite for cross platform F# development.
• Rider - A cross-platform C# IDE based on the IntelliJ platform and ReSharper

Image Processing

• ImageResizer - Add commands to image URLs to get altered versions in milliseconds. Resizing, editing etc of images in real-time.
• ImageProcessor - Open-source .NET library to manipulate images on-the-fly.
• DynamicImage - High-performance open-source image manipulation library for ASP.NET.
• MetadataExtractor - Extracts Exif, IPTC, XMP, ICC and other metadata from image files.
• Emgu CV - Cross-platform .NET wrapper for the OpenCV library.
• DotImaging - Minimalistic .NET imaging portable platform
• Magick.NET - .NET wrapper for the ImageMagick library.

Install tools

• Wix Toolset - The most powerful set of tools available to create your Windows installation experience
• Squirrel - Squirrel is both a set of tools and a library, to completely manage both installation and updating your Desktop Windows application.
• Chocolatey - like yum or apt-get, but for Windows.

Internationalization

• i18n - Smart internationalization for ASP.NET MVC
• MessageFormat.NET - ICU MessageFormat implementation in .NET lets you write contextual UI messages (PCL library)

Interoperability

• CppSharp - Tools to surface C++ APIs to C#
• Sharpen - Sharpen is an Eclipse plugin created by db4o that allows you to convert your Java project into C#
• CXXI - C++ interop framework

IoC

• Castle Windsor - Castle Windsor is best of breed, mature Inversion of Control container available for .NET and Silverlight
• Unity - Lightweight extensible dependency injection container with support for constructor, property, and method call injection
• Autofac - An addictive .NET IoC container
• Ninject - The ninja of .net dependency injectors
• StructureMap - The original IoC/DI Container for .Net
• Spring.Net - Spring.NET is an open source application framework that makes building enterprise .NET applications easier
• LightInject - A ultra lightweight IoC container
• TinyIoC - Single-file, easy and cross-platform IoC container
• Simple Injector - Simple Injector is an easy-to-use Dependency Injection (DI) library for .NET 4+ that supports Silverlight 4+, Windows Phone 8, Windows 8 including Universal apps and Mono.
• Scrutor - Assembly scanning extensions for Microsoft.Extensions.DependencyInjection.

JavaScript Engines

• ClearScript - A library that makes it easy to add scripting to your .NET applications. It currently supports JavaScript (via V8 and JScript) and VBScript.
• Edge.js - Run .NET and Node.js code in-process on Windows, MacOS, and Linux
• Jint - JavaScript interpreter for .NET which provides full ECMA 5.1 compliance and can run on any .NET platform.
• Jurassic - A implementation of the ECMAScript language and runtime. It aims to provide the best performing and most standards-compliant implementation of JavaScript for .NET.

Logging

• Essential Diagnostics - Extends the inbuilt features of System.Diagnostics namespace to provide flexible logging
• NLog - NLog - Advanced .NET and Silverlight Logging
• Logazmic - Open source nlog viewer for Windows
• ELMAH - Official ELMAH site
• Elmah MVC - Elmah for MVC
• Logary - Logary is a high performance, multi-target logging, metric, tracing and health-check library for mono and .Net. .Net's answer to DropWizard. Supports many targets, built for micro-services.
• Log4Net - The Apache log4net library is a tool to help the programmer output log statements to a variety of output targets
• Serilog - A no-nonsense logging library for the NoSQL era. Combines the best of traditional and structured diagnostic logging in an easy-to-use package.
• StackExchange.Exceptional - Error handler used for the Stack Exchange network
• Semantic Logging Application Block (SLAB) - Extends the inbuilt features of System.Diagnostics.Tracing namespace (EventSource class) to log to several sinks including Azure Tables, Databases, files (JSON, XML, text). Supports in-process and out-of-process logging through ETW, and Rx for real-time filtering/aggregating of events.
• Foundatio - A fluent logging api that can be used to log messages throughout your application.
• Exceptionless - Exceptionless .NET Client
• Loupe - Centralized .NET logging and monitoring. [Proprietary] [Free Tier]

Machine Learning and Data Science

• Infer.NET - A framework for running Bayesian inference in graphical models. It can also be used for probabilistic programming. [Free] [Research]
• Accord.NET - Machine learning framework combined with audio and image processing libraries (computer vision, computer audition, signal processing and statistics).
• Accord.NET Extensions - Advanced image processing and computer vision algorithms made as fluent extensions.
• AForge.NET - Framework for developers and researchers in the fields of Computer Vision and Artificial Intelligence (image processing, neural networks, genetic algorithms, machine learning, robotics).
• Deedle - Data frame and (time) series library for exploratory data manipulation with C# and F# support
• FsLab - A collection of data science and machine learning libraries for F# and .NET
• numl - Designed to include the most popular supervised and unsupervised learning algorithms while minimizing the friction involved with creating the predictive models.
• R Provider - Type provider that exposes R packages and functions in a type-safe way to F# callers
• F# Data - F# type providers for accessing XML, JSON, CSV and HTML files (based on sample documents) and for accessing WorldBank data

Markdown Processors

• MarkdownSharp - Open source C# implementation of Markdown processor, as featured on Stack Overflow.
• F# Formatting - Tools for documenting F# and C# projects. The library contains extensible Markdown parser as a core component.
• CommonMark.NET - Implementation of CommonMark specification in C# for converting Markdown documents to HTML. Optimized for maximum performance and portability.
• markdig - A fast, powerful, CommonMark compliant, extensible Markdown processor for .NET.

Mail

• FluentEmail - A Fluent Wrapper for System.Net.Mail with razor templating support.
• MailKit - A complete cross-platform mail stack including IMAP, POP3, SMTP, authentication and more. Built on top of MimeKit.
• MimeKit - A cross-platform .NET MIME creation and parser library with support for S/MIME, PGP, TNEF and Unix mbox spools.
• PreMailer.Net - C# library that moves your stylesheets to inline style attributes, for maximum compatibility with E-mail clients.

Mathematics

• MathNet - Math.NET is an opensource initiative to build and maintain toolkits covering fundamental mathematics, targetting advanced but also every day needs of .Net developers
• UnitConversion - Expansible Unit Conversion Library for .Net Core and .Net Framework

Media

• TagLib# - TagLib# (aka taglib-sharp) is a library for reading and writing metadata in media files, including video, audio, and photo formats
• NAudio - Playback, decode and encode audio in a variety of file formats such as MP3, MP4, WAV, AIFF, Speex, etc.

Metrics

• C# StatsD Client - C# client for Etsy's StatsD
• Foundatio - A common interface with in memory, redis, StatsD, and Metrics.NET implementations.

Micro Framework

• .NET Micro Framework Interpreter - Microsoft® .NET Micro Framework (NETMF) for developing embedded applications on small devices using Visual Studio

Minification

• Microsoft Ajax Minifier - Contains JS and CSS minifiers which have a highest performance, because its have been specifically designed for .NET. Optionally produce Source Maps for JS code.
• Web Markup Minifier - .NET library that contains a set of markup minifiers. The objective of this project is to improve the performance of web applications by reducing the size of HTML, XHTML and XML code.

Misc

• CSharp Pad - A web based C# REPL with awesome code completion.
• AzureCrawler - Take HTML Snapshots for your Angular, Ember, Durandal or any JavaScript applications
• BitSharp - C# Bitcoin Node
• CSScript - CS-Script is a CLR based scripting system which usesC# as a programming language. CS-Script currently targets Microsoft implementation of CLR (.NET 2.0/3.0/3.5/4.0/4.5) with full support on Mono. Comes with many additional features, such as script hosting.
• FlatMapper - A library to import and export data from and to plain text files in a Linq compatible way.
• FluentValidation - A small validation library for .NET that uses a fluent interface and lambda expressions for building validation rules.
• Humanizer - Humanizer meets all your .NET needs for manipulating and displaying strings, enums, dates, times, timespans, numbers and quantities
• LINQPad - a C#/VB/F# scratchpad that instantly executes any expression, statement block or program with rich output formatting and a wealth of features. Also lets you interactively query databases in LINQ. [$]
• Polly - Express transient exception handling policies such as Retry, Retry Forever, Wait andRetry or Circuit Breaker in a fluent manner. (.NET 3.5 / 4.0 / 4.5 / PCL / Xamarin)
• Rant - The Rant Procedural Text Generation DSL http://berkin.me/rant/
• ScriptCS - Write C# apps with a text editor, nuget and the power of Roslyn!
• Shielded - Software Transactional Memory (STM) implementation for .NET
• MSBuild ILMerge task - MSBuild ILMerge task is a NuGet package allows you to use the famous ILMerge utility in automated builds and/or Visual Studio projects.
• ReactJS.NET - ReactJS.NET is a library that makes it easier to use Babel along with Facebook's React and JSX from C#.
• Aeron.NET - Efficient reliable UDP unicast, UDP multicast, and IPC message transport - .NET port of Aeron
• TypeShape - TypeShape is a small, extensible F# library for practical generic programming
• Streams - A lightweight F#/C# library for efficient functional-style pipelines on streams of data.
• MediatR - Simple, unambitious mediator implementation in .NET
• Warden - Define "health checks" for your applications, resources and infrastructure. Keep your Warden on the watch
• ByteSize - ByteSize is a utility class that makes byte size representation in code easier by removing ambiguity of the value being represented. ByteSize is to bytes what System.TimeSpan is to time.
• Jot - a library for persisting and restoring application state (a better alternative to .settings files).

MVVM

• Caliburn.Micro - A small, yet powerful framework, designed for building applications across all XAML platforms. Its strong support for MV* patterns will enable you to build your solution quickly, without the need to sacrifice code quality or testability.
• MVVM Light Toolkit - The main purpose of the toolkit is to accelerate the creation and development of MVVM applications in WPF, Silverlight, Windows Store (RT) and for Windows Phone
• Catel - Catel is an application development platform with the focus on MVVM (WPF, Silverlight, Windows Phone and WinRT) and MVC (ASP.NET MVC). The core of Catel contains an IoC container, models, validation, memento, message mediator, argument checking, etc.
• UpdateControls - Update Controls does not require that you implement INotifyPropertyChanged or declare a DependencyProperty. It connects controls directly to CLR properties. This makes it perfect for the Model/View/ViewModel pattern.
• ReactiveUI - An MVVM framework for .NET that integrates the Reactive Extensions (Rx) framework, enabling developers to build elegant, testable applications using WPF, Windows Store Apps, WP8 or Xamarin.
• Okra App Framework - An app centric MVVM framework for Windows 8.1 built with dependency injection in mind, including a full set of Visual Studio MVVM templates.
• Prism - A cross-platform desktop and mobile MVVM development framework.
• WPF Application Framework (WAF) - A lightweight Framework that helps you to create well structured WPF Applications. It supports you in applying a Layered Architecture and the Model-View-ViewModel pattern.
• MVVMCross - Cross-platform mvvm mobile development framework for WPF, Silverlight for WP7 and WP8, Mono for Android, MonoTouch for iOS, Windows Universal projects (WPA8.1 and Windows 8.1 Store apps). Makes extensive use of Portable Class Libraries (PCL) to provide maintainable cross platform C# native applications.
• Stylet - Minimal MVVM framework inspired by Caliburn Micro, with good documentation, high test coverage, and its own IoC container
• Gemini - IDE framework similar in concept to the Visual Studio Shell. Built on WPF, AvalonDock, and Caliburn Micro.

Object to object mapping

• TinyMapper - A tiny and quick object mapper for .Net.
• ExpressMapper - A lightweight, lighting fast .Net mapper to map one type of object(s) to another in automated and easy way. ExpressMapper relies completely on the expression trees.

Office

• ExcelDna - ExcelDna makes it easier to create and deploy Excel Add-Ins using C#, F# or VB .NET
• ClosedXML - ClosedXML makes it easier for developers to create Excel 2007/2010 files
• NPOI - This project is the .NET version of POI Java project at http://poi.apache.org/.
• EPPlus - EPPlus is a .net library that reads and writes Ex