I think that this will expand the variety of apps and it will be great for small/medium firms you have legacy software developed in .net and couldn't afford to start over from scratch. With this move they can port their software to Linux and Mac and maybe also extend into mobile apps.
Visual Studio and .NET Go Cross-Platform | Visual studio content from Paul Thurrott's SuperSite for Windows
In a major expansion of its open source efforts, Microsoft announced today that will open up Visual Studio and .NET to developers on all major platforms. It starts with the open-sourcing of the core .NET server stack, a new free and full-featured Visual Studio edition, and preview versions of ...