The dotnet repository is the starting point to engage in and learn about .NET open source projects from Microsoft and the .NET Foundation. You can read the more detailed post .NET Core is Open Source on the .NET blog.

There are many open source .NET projects, a few of which are listed below. Additionally @quozd maintains a list of awesome open source .NET libraries, tools, frameworks, and software. ASP.NET Core (and .NET Core) Library and Framework Support is listed at ANCLAFS.com.

• .NET Compiler Platform ("Roslyn")
• .NET Core
• ASP.NET Core
• EntityFramework
• Orleans
• Exceptionless
• Glimpse
• JSON.NET
• Mobius: C# API for Apache Spark
• MonoGame
• Mono Project
• MVVM Cross
• MVVM Light Toolkit
• ReactiveUI

For a longer list, see:

• .NET developer projects
• .NET consumer projects

For a list of free services and tools for open source .NET projects, see:

• Free Services & Tools for Open Source .NET Projects

.NET open source projects from Microsoft (gladly) accept PRs and other contributions. To contribute to ASP.NET Core or Entity Framework Core, see the ASP.NET Contributing Guide. To contribute to .NET Core, see the .NET Core Contributing Guide.

You are also encouraged to start a discussion by posting on the .NET Foundation Forums or filing an issue in the corresponding GitHub project. See the contributing guides for more details.

Most .NET open source projects at Microsoft have been contributed to the .NET Foundation. There are two main .NET Foundation projects for Microsoft open source projects: ASP.NET Core project and the .NET Core project.

.NET open source projects typically use either the MIT or Apache 2 licenses for code. Some projects license documentation and other forms of content under Creative Commons Attribution 4.0. See specific projects to understand the license used.