Microsoft is now the leading company for open source contributions on GitHub
It seems to me like they are only open sourcing the products they wish more people are using, and not their actually useful products like MSOffice and the Windows OS.Edit: to be clear, I know it is in their best interest not to open source those products, because that's where most of their money comes from. But it really looks to me like the want to flood the market with random open source stuff, so that they seem more open source friendly. But in reality they are not actually contributing anything very useful to the community.