TypeScript in Visual Studio.
With so many existing options, why would Microsoft decide to set foot into this arena?
The answer is that it is a simple case of tooling.
TypeScript's playground: not bad for a text area in a browser.
With language aficionado Anders Hejlsberg leading the charge, it will surely throw up some good concepts and thought bubbles, regardless of whether the language itself gains traction or not.
To give TypeScript a test run, have a quick hack in the TypeScript playground.