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.
Visual Studio Code is just a re-branded Atom editor [1] bundled with atom plugins, such as OmniSharp [2]. And while Atom is impressive, that's not Microsoft's doing, plus they took an open-source project and released something which isn't open-source and named that in a way to make people believe that Visual Studio is now all of a sudden cross-platform. Well, I think I'll pass for now.
Rebranding or not, doesn't matter (A lot of mainstream projects out there start like that). The point is that they are pushing to be a company that supports a cross platform development, so I'm surprised that you'd even bring that point. Also, CoreCLR and .Net are their own, and no, unlike what you think, they aren't going anywhere so soon.
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.