2. Novell
3. Intel
4. Red Hat
So how did we get here? Microsoft designed Hyper-V for running Linux based operating systems under Windows Server. But, they appropriated GPL code to do it. Not a problem as long as they only run the code inside Microsoft. But Hyper-V is a publicly used product They got caught and chose to release 20,000 lines of code as opensource software rather than risk being convicted of copyright infringement. Giving up code was damage done to MS (by their point of view), but they decided to make the best of things and promised to actually help out with the Linux kernel (for their own benefit). They wanted to make it easier and faster to run Linux on Windows. But the GPL cooperation process also makes it easier to run Windows on Linux, which they don't like. For a while it looked like they were going to back out. But in the last few days, there was an explosion of activity from Microsoft. Bumping them up from a barely contributor to 5th place contributer (measures in working hours), ahead of even Google.
So how is this related to videogames? Well, only one of the top 5 contributers developers and publishes videogames. Gamers should be watching.