They have made .Net & CoreCLR open source (including the compiler, runtime and libraries), enabled Visual Studio to do more than developing just Windows applications (they now allow developing Android/iOS apps as well) and are trying to make developing for other platforms even easier with VS 2015.
Not only that, they just released a cross platform Code Editor which works on Windows, Linux and Mac, called 'Visual Studio Code'. That and more was announced in the Build Conference held recently.