[ppog]

I think MichaelGG is thinking of the Rotor "shared source" implementation for BSD, which was released around the same time as .NET for Windows as a proof of concept for implementing the .NET standards on other platforms. (These standards included CIL and the Common Type System, not just C#.) But as Michael says though it fell way short of full .NET, lacking many libraries and a lot of the optimisations of the Windows .NET implementation; and it wasn't open source in that you couldn't fork it, you could only look at the code 'under glass.'