Microsoft is feeling the effect of the EU's various judgements on them the past few years, and is choosing to start releasing source code for their Windows Server operating systems. Of course, they aren't just giving it away - you have to license it. Developers and companies can purchase licenses to view source code for integration or development purposes.
"This action goes far beyond compliance with the European Commission's March 2004 decision and exceeds Microsoft's legal obligations to provide companies with the technical specifications of its proprietary communications protocols, the company said. A reference license to the Windows Server source code will provide software developers with the most precise and authoritative description possible of the Windows protocol technologies, Microsoft noted."
Microsoft's business practices have been under scrutiny for a long time, and this road was one well worn. Microsoft had to relent eventually, though it was more of a time-buying move if anything. The details of the licenses aren't fully public yet, and it may be a "look but don't touch" policy that can restrict how people develop around the new information. Time will tell.