"test some part of C#" - Snippet Compiler already works well for this, if you don't want to start Visual Studio.

Snippet Compiler isn't broken, though, like STFU is. For instance, I have the .NET framework in C:\WINNT.

Besides, for command line use, how hard is it to:

1. Start menu, Visual Studio Command Prompt 2. vim temp.cs 3. csc temp.exe 4. temp.exe