Mono Tools for Visual Studio is released to a limited number of developers. The first release integrates four pieces of functionality into Visual Studio:

-Mono Migration Analzyer (MoMA), scanning projects for incompatibilities and helping developers work through issues.
-Run on Mono for Windows, testing against Mono on Windows to help isolate issues arising from differences between Mono and .Net.
-Run on Mono on Linux, testing against Mono on Linux to work through differences between Windows and Linux.
-Debug on Mono on Linux, for remote debugging of Mono applications on Linux.

More info: Mono Tools for Visual Studio