This must have been some time ago. The .NET runtime / C# compiler you're thinking of is Rotor, a version of the runtime for educational use released back in 200

This must have been some time ago. The .NET runtime / C# compiler you're thinking of is Rotor, a version of the runtime for educational use released back in 2006. Mono has followed the official implementation quite closely for at least the past decade. The new official C# compiler - Roslyn - was released in 2014. It's open source and cross-platform. It was followed up same year by .NET Core, which is the new primary distribution of .NET with support for Windows, Linux, macOS and a handful of [other] BSD derivatives. Sources: https://github.com/dotnet/roslyn https://github.com/dotnet/roslyn https://github.com/dotnet/coreclr https://github.com/dotnet/coreclr https://github.com/dotnet/corefx https://github.com/dotnet/corefx Binaries: https://dotnet.microsoft.com/download https://dotnet.microsoft.com/download