Are you interested in the recent move by Microsoft to release the Visual Basic and C# compilers as open source? Both languages were created by Microsoft (Visual Basic in 1991 and C# in 2000) as part the .NET Framework. The .NET Framework is still proprietary, but open source compilers for C# and VB have been created by others. Recently Microsoft has released its own open source .NET compiler platform (called Roslyn) which provides compilers for both languages.
You can download the source here.