With other languages such as Java and Python getting large user base, this is a good move to gain some users.

Microsoft is open sourcing .NET, this should reduce the compatibility challenges with cross-platform applications developed using Microsoft Tools.

http://news.microsoft.com/2014/11/12/microsoft-takes-net-open-source-and-cross-platform-adds-new-development-capabilities-with-visual-studio-2015-net-2015-and-visual-studio-online/