OpenJDK is unofficially ported and built for numerous platforms. But OpenJDK is Oracle's JDK. To contribute to it, you sign Oracle's contributor's license agreement.

Oracle's no golden example as a leader in open source (let alone libre software), but they demonstrate the probable trajectory for the Microsoft projects at this point: a healthy, cohesive community of developers (developers!) using the technology in an ever increasing number of projects and platforms.