open-sourcing of many of their developer tools and other stuff
Most if it isn't really OSS, it's a "look, but don't touch" un-compilable reference.
They had to do something in order to remain vaguely relevant to developers (plus anything in .NET is decompilable anyway). I do appreciate the very little they've done, however. I won't begrudge them credit for it, the few decent MS devs must have lobbied hard for that. (Although it's funny how you get the MS-only nerds whining how shite OSS is, when at the same time MS are convincing them they're now an OSS company)
Their "real" products, however, are still as closed tight as a nun's crunt. VS? Office? NTFS? IE? No chance!