SharpLang – Compiles C# & .NET to native machine code, using LLVM as a backend.
Platforms
Castle Project – Umbrella project for ActiveRecord, DynamicProxy, MonoRail, Windsor
Catel – Application platform with IoC, logging, reflection and much more that serves as a base for applications that must be ready for future growth.
Enterprise Web Library (EWL) – An extremely opinionated platform for web applications that trades off performance, scalability, and development flexibility for an ease of maintenance you won’t find anywhere else.Enterprise Web Library site.
KonfDB – Configuration Management as a Service for cross-platform, multi-tenant enterprise/hobby applications.
Languages
Boo – A .NET language similar to Python but with static typing, and many meta-programming capabilities.
ClojureCLR – A .NET implemention of the Clojure programming language, built on the DLR.
Cobra – 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
DotLiquid – .NET Port of Tobias Lütke’s Liquid template language.
Eagle – A .NET implementation of the Tcl programming language, built on the CLR.
Essence# – 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.
F# – A mature, open source, cross-platform, functional-first programming language.
F* – An ML-like language with a type system for program verification.
IronScheme – A R6RS conforming Scheme-like implementation based on the Microsoft DLR.
Irony – a development kit for implementing languages on .NET platform
MoonSharp – A Lua interpreter and remote debugger, written entirely in C#, easily embeddable in any application running on .NET 3.5+ and Mono.
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 – A .NET implementation of the ECMAScript language and runtime.
Phalanger – 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.
MahApps.Metro – A toolkit for creating metro-style WPF applications.
Math.NET Numerics – Provides methods and algorithms for numerical computations in science, engineering and every day use.
Mathos Core Libary – A library with algorithms for numerical calcultations in finance, statistics, pattern recognition, and more.
Mathos Parser – A simple parser for mathematical expressions before and at runtime.
MimeKit – A cross-platform .NET MIME creation and parser library with support for S/MIME, PGP, DKIM, TNEF and Unix mbox spools.
Mjolnir – Hystrix-inspired fault tolerance with circuit breakers and thread pools.
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.
NAudio – An open source .NET audio and MIDI library.
NPOI – An Office file formats (xls, xlsx, docx) read/write library for .NET
OneDriveRestAPI – OneDrive .Net Client Library using the REST API.
Orleans – 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.
AForge.NET – a C# framework designed for developers and researchers in the fields of Computer Vision and Artificial Intelligence – image processing, neural networks, genetic algorithms, machine learning, robotics
SharpNLP – SharpNLP is a collection of natural language processing tools written in C#
Toxy – An data/text extraction framework for .NET, similar to Tika in Java.
Graphics & Server-side Image Processing
DynamicImage – WPF-based server-side image rendering system – lots of visual effects implemented as high-performance shaders. Has URL api, several plugins available.
ImageProcessor – A .NET Library For On-The-Fly Processing Of Images (GDI+ based).
ImageResizer – 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.
OpenTK – OpenTK is a low-level, cross-platform binding to OpenGL, OpenGL ES, OpenCL and OpenAL, available for Windows, Linux, Mac OS X, BSD, Android and iOS.
SharpDX – SharpDX is a project delivering the full DirectX API for .NET on all Windows platforms.
Logging
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 – 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.
log4net – A tool to help the programmer output log statements to a variety of output targets.
LogMaster4Net – It is a central log server which can organize your logs in different applications in a same place but have same log behaviors (loggers, appenders, levels and rules) like in the indepedent applications before.
NLog – NLog is a free logging platform for .NET with rich log routing and management capabilities.
Serilog – Serilog combines the best features of traditional and structured diagnostic logging in an easy-to-use package.
Model-View-ViewModel (MVVM) Frameworks
Caliburn Micro – A small, yet powerful framework, designed for building applications across all XAML platforms.
Catel.MVVM – Catel is an application development platform with the focus on MVVM.
MVVM Cross – A cross-platform mobile MVVM development framework.
MVVM Extensions – MVVM cross platform (.NET FW 4.5, WPF, Windows Runtime/Phone) extensions for .NET with support for async commands, MVVM-friendly Object and Task with support for UI notification.
MVVM Light Toolkit – A cross-platform desktop and mobile MVVM development framework.
Okra App Framework – An MVVM framework for Windows Store applications including MVVM templates for Visual Studio.
Radical – An infrastructure framework whose primary role is to help in the development of composite WPF/Silverlight/WP/WinRT applications based on the Model View ViewModel pattern.
ReactiveUI – An MVVM framework that integrates with the Reactive Extensions for .NET to create elegant, testable User Interfaces that run on any mobile or desktop platform.
Simple Mvvm Toolkit – Provides a simple framework and set of tools for getting up to speed quickly with applications based on the MVVM design pattern.
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.
Tools
Cake (C# Make) – A build automation system with C#/Roslyn driven build scripts.
CodeContracts – Source code for the CodeContracts tools for .NET
CodeMaid – an open source Visual Studio extension to cleanup, dig through and simplify our C#, C++, F#, VB, PHP, JSON, XAML, XML, ASP, HTML, CSS, LESS, SCSS, JavaScript and TypeScript coding.
FsPickler – Serialization library that facilitates the distribution of .NET objects.
GitLink – Command-line tool to make .NET open source accessible without the need for a symbols server
GitVersion – Use convention to derive a SemVer product version from a GitFlow based repository.
Glimpse – Providing real time diagnostics & insights to the fingertips of hundreds of thousands of developers daily.
ILSpy – ILSpy is the open-source .NET assembly browser and decompiler.
Mini Profiler – A simple but effective mini-profiler for .NET.
Obfuscar – MSIL obfuscation utility for .NET assemblies.
OmniSharp– OmniSharp is a family of Open Source projects, each with one goal: To enable a great .NET experience in YOUR editor of choice
Outcomes.Net – Fluent wrapper that eliminates plumbing code around failure-prone functions.
Paket – Dependency manager for .NET and Mono projmects, which is designed to work well with NuGet packages and also enables referencing files directly from GitHub repositories.
Protobuf-net – A .NET implementation of protobuf, allowing you to serialize your .NET objects efficiently and easily.
scriptcs – scriptcs makes it easy to write and execute C# with a simple text editor.
ZeroToNine – A tool for maintaining .NET Assembly versions across multiple files.
Testing
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.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 – White is a framework for automating rich client applications based on Win32, WinForms, WPF, Silverlight and SWT (Java) platforms.
xUnit – xUnit.net is a community-focused unit testing tool for the .NET Framework.
Dependency Injection
Autofac – Autofac is an addictive Inversion of Control container for .NET 4.5, Silverlight 5, Windows Store apps, and Windows Phone 8 apps.
Castle Windsor – A mature Inversion of Control container available for .NET and Silverlight
DI Feature Tests – Tests that track commmon DI features among multiple containers
dI.Hook – DI container that allows invocation using AOP
DryIoc – DryIoc is small, fast, capable IoC Container for .NET
fFastInjector – fFastInjector is a high-performing dependency injector, service locator, and/or IOC (inversion of control) container.
MicroSliver – MicroSliver is a micro, non-bloat, non-intimidating and speedy .NET (ASP.NET, Silverlight, RIA Services, WPF, Forms and Metro!)
Mugen Injection – 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 – QuickInject is a Unity 3.5 based IoC container that aims to give the Unity container a performance advantage in basic scenarios.
Simple Injector – 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 – Spring.NET is an open source application framework that makes building enterprise .NET applications easier.
StructureMap – 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 – Style MVVM is a toolkit designed for the Windows Store platform around the idea of being light weight and fast.
TinyIoC – An easy to use, hassle free, Inversion of Control Container for small projects, libraries and beginners alike.
Unity Container – The Unity Container (Unity) is a lightweight, extensible dependency injection container with optional support for instance and type interception.
Data Access
Dapper – Dapper is a single file you can drop in to your project that will extend your IDbConnection interface.
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.
Simple Data – A light-weight, dynamic data access component for C# 4.0.
Sqlite-net – Simple, powerful, cross-platform SQLite client and ORM.
NMEA Parser – Library for handling NMEA message in Windows Desktop, Store, Phone and Xamarin (Android + iOS), coming from files, Bluetooth, serial port or any stream.
Warewolf Easy Service Bus – An open source easy to use service bus, built on numerous .Net technologies including WF (Windows Workflow Foundation), SignalR and WPF.
Distributed Caching and Computing
CacheAdapter – a .Net library allows developers to use unified-implemented cahce provider
Dache – An open source distributed caching service, built on .NET 4.0 and using TCP sockets for communication.
Windows Workflow
Workflow Extractor – Document Windows Workflow logic into a Word document or Excel sheet.
