This community maintained list showcases .NET open source developer projects. It is intended to include projects that are useful for any aspect of the development process. For consumer projects, see the [.NET open source consumer projects list](dotnet-consumer-projects.md). PR a change into either list and it will be accepted (modulo duplicates).
Please sort projects alphabetically and provide a one-line description. GitHub/CodePlex (or other source) links are preferred, but feel free to also include marketing sites. Create new sections, as appropriate.
* [Catel](http://catelproject.com/) - Application platform with IoC, logging, reflection and much more that serves as a base for applications that must be ready for future growth.
* [ClojureCLR](https://github.com/clojure/clojure-clr) - A .NET implemention of the [Clojure](http://clojure.org) programming language, built on the DLR.
* [Cobra](http://cobra-language.com/) - Clean, high-level syntax (Boo/Python-like). Static and dynamic binding. First class support for unit tests and contracts. Compiled performance with scripting conveniences. Lambdas and closures. Extensions and mixins
* [Essence#](https://essencesharp.codeplex.com/) - Essence# is a fully dynamic and highly polymorphic programming language which features pervasive message passing, pervasive dynamic and strong typing, pervasive and deep reflection and pervasive object orientation.
* [MoonSharp](http://www.moonsharp.org) - A Lua interpreter and remote debugger, written entirely in C#, easily embeddable in any application running on .NET 3.5+ and Mono.
* [Nemerle](https://github.com/rsdn/nemerle) - A high-level statically-typed programming language which offers functional, object-oriented and imperative features and has a simple C# like syntax and a powerful meta-programming system.
* [NiL.JS](https://github.com/nilproject/NiL.JS) - A .NET implementation of the ECMAScript language and runtime.
* [Phalanger](http://www.php-compiler.net/) - full-featured PHP runtime & compiler for .NET/Mono frameworks. Phalanger is modern open-source implementation of PHP, compatible with the vast array of existing PHP code.
* [NemerleWeb](https://github.com/NemerleWeb/NemerleWeb) - Web MVVM library for .Net. It uses reactive data model which allows creating rich internet applications.
* [Albedo](https://github.com/ploeh/Albedo) - A .NET library targeted at making Reflection programming more consistent, using a common set of abstractions and utilities.
* [AngleSharp](https://github.com/FlorianRappl/AngleSharp) - Ultimate angle brackets parser library. It parses HTML5, MathML, SVG and CSS to construct a DOM based on the official W3C specification.
* [ArcGIS.PCL](https://github.com/davetimmins/ArcGIS.PCL) - Call ArcGIS Server REST API resources. You can also convert between ArcGIS features and GeoJSON.
* [Argument](https://github.com/ashmind/Argument) - Argument validation microframework that does one thing in the simplest way possible.
* [AshMind.Extensions](https://github.com/ashmind/ashmind-extensions) - A set of very conservative extension methods most of which closely follow naming and design patterns of .NET Base Class Library.
* [ComparerExtensions](https://github.com/jehugaleahsa/comparerextensions) - Build IComparer and IEqualityComparer objects using natural language syntax.
* [DotNetOpenAuth](https://github.com/DotNetOpenAuth) - Library that adds support for your site visitors to login with their OpenIDs by just dropping an ASP.NET control onto your page.
* [FluentValidation](https://github.com/JeremySkinner/FluentValidation) - A small validation library for .NET that uses a fluent interface and lambda expressions for building validation rules.
* [Math.NET Numerics](http://numerics.mathdotnet.com/) - Provides methods and algorithms for numerical computations in science, engineering and every day use.
* [Mathos Core Libary](http://mathos.codeplex.com/) - A library with algorithms for numerical calcultations in finance, statistics, pattern recognition, and more.
* [Mathos Parser](http://mathosparser.codeplex.com/) - A simple parser for mathematical expressions before and at runtime.
* [MoreLINQ](https://code.google.com/p/morelinq/) - LINQ to Objects is missing a few desirable features. This project will enhance LINQ to Objects with extra methods, in a manner which keeps to the spirit of LINQ.
* [WebApiProxy](https://github.com/faniereynders/WebApiProxy) - An automatic proxy provider for RESTful services built on ASP.NET Web API. Includes JavaScript & C# client generation.
* [XamlEssentials](https://github.com/AdvancedREI/XamlEssentials) - Collection of helpers for Microsoft's XAML platforms.
* [Zlib.Portable](https://github.com/AdvancedREI/Zlib.Portable) - A Portable Class Library port of the Zlib library from http://dotnetzip.codeplex.com.
* [DynamicImage](https://github.com/tgjones/dynamic-image) - WPF-based server-side image rendering system - lots of visual effects implemented as high-performance shaders. Has URL api, several plugins available.
* [ImageProcessor](http://imageprocessor.org/) - A .NET Library For On-The-Fly Processing Of Images (GDI+ based).
* [ImageResizer](http://imageresizing.net/) - Add commands to image URLs to get altered versions in milliseconds. Edit, filter, touch-up images in real-time. (multiple backends - FreeImage, C++/CLI, GDI+, WIC). 45+ plugins available.
* [Exceptionless](https://github.com/exceptionless/Exceptionless) - Provides real-time .NET error reporting for your ASP.NET, Web API, WebForms, WPF, Console, and MVC apps. It organizes the gathered information into simple actionable data that will help your app become exceptionless!
* [ELMAH](https://code.google.com/p/elmah/) - ELMAH (Error Logging Modules and Handlers) is an application-wide error logging facility that is completely pluggable. It can be dynamically added to a running ASP.NET web application, or even all ASP.NET web applications on a machine, without any need for re-compilation or re-deployment.
* [Obfuscar](https://obfuscar.codeplex.com) - MSIL obfuscation utility for .NET assemblies.
* [Outcomes.Net](https://github.com/kinetiq/Ether.Outcomes/) - Fluent wrapper that eliminates plumbing code around failure-prone functions.
* [Paket](http://fsprojects.github.io/Paket/) - Dependency manager for .NET and Mono projects, which is designed to work well with NuGet packages and also enables referencing files directly from GitHub repositories.
* [Protobuf-net](https://code.google.com/p/protobuf-net/) - A .NET implementation of protobuf, allowing you to serialize your .NET objects efficiently and easily.
* [scriptcs](http://scriptcs.net/) - scriptcs makes it easy to write and execute C# with a simple text editor.
* [Snoop WPF](https://github.com/cplotts/snoopwpf) - Snoop - The WPF Spy Utility
* [AutoFixture](https://github.com/AutoFixture/AutoFixture) - An open source framework for .NET designed to minimize the 'Arrange' phase of your unit tests. Its primary goal is to allow developers to focus on what is being tested rather than how to setup the test scenario, by making it easier to create object graphs containing test data.
* [TestStack.FluentMvcTesting](https://github.com/TestStack/TestStack.FluentMVCTesting) - Simple, terse, fluent unit testing for ASP.NET MVC Controllers.
* [TestStack.Seleno](https://github.com/TestStack/TestStack.Seleno) - Seleno helps you write automated UI tests in the right way by implementing Page Objects and Page Components and by reading from and writing to web pages using strongly typed view models.
* [TestStack.White](https://github.com/TestStack/White) - White is a framework for automating rich client applications based on Win32, WinForms, WPF, Silverlight and SWT (Java) platforms.
* [Autofac](http://autofac.org/) - Autofac is an addictive Inversion of Control container for .NET 4.5, Silverlight 5, Windows Store apps, and Windows Phone 8 apps.
* [DryIoc](https://bitbucket.org/dadhi/dryioc) - DryIoc is small, fast, capable IoC Container for .NET
* [fFastInjector](https://ffastinjector.codeplex.com/) - fFastInjector is a high-performing dependency injector, service locator, and/or IOC (inversion of control) container.
* [HaveBox](https://bitbucket.org/Have/havebox/wiki/Home) - HaveBox is a very fast and lightweight IoC containter. The goal is to keep it fast and light, and at the same time easy to use.
* [Hiro](https://github.com/philiplaureano/Hiro) - An ultra-lightweight, inversion of control container compiler framework
* [IfInjector](https://github.com/iamahern/IfInjector) - High performance mobile micro-IoC container.
* [LightCore](http://lightcore.ch/de/default.aspx) - LightCore is a lightweight dependency injection container that can be used as a service locator and despite its simplicity and ease boasts numerous features.
* [LightInject](https://github.com/seesharper/LightInject) - A ultra lightweight IoC container
* [MicroSliver](https://microsliver.codeplex.com/) - MicroSliver is a micro, non-bloat, non-intimidating and speedy .NET (ASP.NET, Silverlight, RIA Services, WPF, Forms and Metro!)
* [Mugen Injection](http://mugeninjection.codeplex.com/) - The MugeniInjection is a lightweight and fast managed IoC (Inversion of Control) and DI (Dependency Injection) with support for constructor, property and method call injection
* [QuickInject](https://github.com/isabgol/QuickInject) - QuickInject is a Unity 3.5 based IoC container that aims to give the Unity container a performance advantage in basic scenarios.
* [Simple Injector](https://simpleinjector.org/index.html) - Simple Injector is an easy-to-use Dependency Injection library for .NET 4+ that supports Silverlight 4+, Windows Phone 8, Windows 8 including Universal apps and Mono.
* [Spring.NET](http://www.springframework.net/) - Spring.NET is an open source application framework that makes building enterprise .NET applications easier.
* [StructureMap](http://docs.structuremap.net/) - StructureMap is a Dependency Injection / Inversion of Control tool for .Net that can be used to improve the architectural qualities of an object oriented system by reducing the mechanical costs of good design techniques.
* [StyleMVVM](https://stylemvvm.codeplex.com/) - Style MVVM is a toolkit designed for the Windows Store platform around the idea of being light weight and fast.
* [TinyIoC](https://github.com/grumpydev/TinyIoC) - An easy to use, hassle free, Inversion of Control Container for small projects, libraries and beginners alike.
* [Unity Container](http://msdn.microsoft.com/library/ff647202.aspx) - The Unity Container (Unity) is a lightweight, extensible dependency injection container with optional support for instance and type interception.
* [Dapper](https://github.com/StackExchange/dapper-dot-net) - Dapper is a single file you can drop in to your project that will extend your IDbConnection interface.
* [Eggado](https://code.google.com/p/eggado/) - Eggado takes generics, lambdas, expression trees, dynamic methods and DLR and uses them to breathe new life into data access using good old ADO.NET. It's for folks who can live with a SQL dialect.
* [King.Mapper](https://github.com/jefking/King.Mapper) - High performance model mapping.
* [linq2db](https://github.com/linq2db/linq2db/) - Lightweight ORM and LINQ provider with support for various databases including MS SQL, PostgreSQL, Oracle and MySQL
* [Simple Data](https://github.com/markrendle/Simple.Data) - A light-weight, dynamic data access component for C# 4.0.
* [Sqlite-net](https://github.com/praeclarum/sqlite-net) - Simple, powerful, cross-platform SQLite client and ORM.
* [NMEA Parser](https://github.com/dotMorten/NmeaParser) - Library for handling NMEA message in Windows Desktop, Store, Phone and Xamarin (Android + iOS), coming from files, Bluetooth, serial port or any stream.
* [SQL LocalDB Wrapper](https://github.com/martincostello/sqllocaldb) - SQL LocalDB Wrapper is an assembly providing interop with the SQL LocalDB native API from managed code using .NET APIs.
* [RoundHouse](https://code.google.com/p/roundhouse/) - RoundhousE is a Database Migration Utility for .NET using sql files and versioning based on source control
* [Warewolf Easy Service Bus](https://github.com/Warewolf-ESB/Warewolf-ESB) - An open source easy to use service bus, built on numerous .Net technologies including WF (Windows Workflow Foundation), SignalR and WPF.
This list is just a starting point - also take a look at all the projects on [CodePlex](http://www.codeplex.com/) and on [GitHub Trending C#](https://github.com/trending?l=csharp).
[@quozd](http://twitter.com/quozd "@quozd on Twitter") hosts an [Awesome .NET!](https://github.com/quozd/awesome-dotnet) list. Also worth checking out.
