https://github.com/dotnet/dotnet exists for "complete" source build that stitches together SDK, Roslyn, runtime and other dependencies. In fact, it is required by certain Linux distributions for publishing in their feeds, to be built from source in full. All components above can be built and used individually (usually), which is what contributors also do. For example, you can clone and build https://github.com/dotnet/runtime and use the produced artifacts to execute .NET assemblies or build .NET binaries.