Microsoft CaaS Roslyn - Compiler as a Service that is (codebetter.com)

Until now, the VB and C# compilers have been used as black boxes. You put text in, and you get out a binary file. In CodeName Roslyn, we’re changing that dynamic by building an API that exposes compilers’ analysis engine, and opening a world of new scenarios including REPL, write-your-own refactorings, C# and VB as scripting languages, and taking .NET to the cloud.