xUnit.net is a free, open source, community-focused unit testing tool for the .NET Framework.

Every programmer needs a rubberduck. COM add-in for the VBA & VB6 IDE (VBE).

Linq to database provider.

ML.NET is an open source and cross-platform machine learning framework for .NET.

The best C# command line parser that brings standardized *nix getopt style, for .NET. Includes F# support

💫 NClient is an automatic type-safe .Net HTTP client that allows you to call web service API methods using annotated interfaces or controllers without boilerplate code.

Open Source Web Application Framework for ASP.NET Core

Headless Chrome .NET API

Lean Algorithmic Trading Engine by QuantConnect (Python, C#)

Build Mobile, Desktop and WebAssembly apps with C# and XAML. Today. Open source and professionally supported.

.NET core API Gateway

EF Core is a modern object-database mapper for .NET. It supports LINQ queries, change tracking, updates, and schema migrations.

A wrapper executable that can run any executable as a Windows service, in a permissive license.

Google's Material Design in XAML & WPF, for C# & VB.Net.

.NET for Apache® Spark™ makes Apache Spark™ easily accessible to .NET developers.

Mono open source ECMA CLI, C# and .NET implementation.

ASP.NET Core is a cross-platform .NET framework for building modern cloud-based web applications on Windows, Mac, or Linux.

Highly performant and modular controls for node-based editors designed for data-binding and MVVM.

AutoFixture is an open source library for .NET designed to minimize the 'Arrange' phase of your unit tests in order to maximize maintainability. 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.

Command line parsing, invocation, and rendering of terminal output.

One framework for creating powerful cross-platform games.

Powerful .NET library for benchmarking

:cake: Cake (C# Make) is a cross platform build automation system.

An open source fork of Windows Live Writer

Accept Bitcoin payments. Free, open-source & self-hosted, Bitcoin payment processor.

A cross-platform plotting library for .NET