Microsoft is letting developers download the preview version of Visual Studio 2014, due for release by 2015, for developer feedback. The community technology preview (CTP) is available for download here. It will work with Roslyn, the .NET Compiler Platform, that Microsoft open-sourced at the April Build conference this year. Roslyn exposes the Microsoft Visual Basic and C# compilers as APIs.
You can find out more about Roslyn in this MSDN blog post.