Below are the main repos you can use to file bugs and feature requests for .NET. Please try to find the repo that is most closely related to your issue. But don't sweat it too much -- we'll transfer the issue to the appropriate repo should you get it wrong.
.NET Framework
Report isssues to .NET Framework Developer Community
.NET Framework Docker images
.NET Core
Runtimes and libraries
.NET Core home repository
.NET Core runtime, runtime installers, application model, & Base Class Library (BCL)
.NET documentation
.NET API documentation
.NET extension APIs (DI, logging, configuration, etc.)
.NET Core Docker images
.NET Standard definition
WCF client libraries
Entity Framework (EF) and data access
EF Core
EF 6
EF Core & EF 6 documentation
SqlClient data provider for SQL Server
Client UI
Windows Forms
Windows Presentation Foundation (WPF)
.NET Multi-platform App UI
Web
ASP.NET Core framework
ASP.NET Core documentation
ASP.NET 4.x documentation
ASP.NET Core code generators
MSBuild tasks & targets for ASP.NET Core apps
Languages
Roslyn (C# / VB compiler)
C# suggestions, specification, ongoing language design
VB suggestions, specification, ongoing language design
The F# compiler, FSharp.Core library, and tools for F#
RFCs and docs related to the F# language design process
F# language and FSharp.Core library suggestions
Tooling and SDK
Visual Studio project system for C#, F#, & VB
.NET Core SDK (used by Visual Studio & .NET Core CLI)
.NET Core installer (produces zips, tarballs, and installers for the .NET SDK)
Templating engine used by dotnet new
.NET Core unit testing project templates
Build platform for .NET & Visual Studio
NuGet client
NuGet.org
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