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

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.

.NET API Gateway

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

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

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

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

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

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

Mutation testing for .NET core and .NET framework!

Powerful .NET library for benchmarking

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

Open Source Web Application Framework for ASP.NET Core. Offers an opinionated architecture to build enterprise software solutions with best practices on top of the .NET and the ASP.NET Core platforms. Provides the fundamental infrastructure, production-ready startup templates, application modules, UI themes, tooling, guides and documentation.

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

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