From http://news.cnet.com/8301-30684_3-20013546-265.html, I give you this statement by someone unfamiliar with Java and the reasons for other implementations of the technology.
Of course, Java has been forked and fragmented many times over the years, destroying the “write once run anywhere” promise of the technology with different implementations on different computing platforms.
I worked on one such implementation some time ago, GNU Classpath, and the primary reason it came to be was that working with Sun would have required giving up software freedom, our ability to find and fix bugs as we encountered them, and to release those changes as we saw fit. At no point was Classpath interested in fragmenting Java, a big goal was to be 100% compatible.
At some point, the Apache project Harmony, which is what Google uses, came to be via the donations of Intel and IBM. Despite the project name, harmony never came between this project and Classpath. I cannot say how “clean room” the Harmony code is, or how clean the Google VM is. There are obvious performance gains in bytecode that Sun managed to patent thus preventing any other VM from implementing legally.
These things typically end with both sides in a patent sharing agreement to avoid mutually assured destruction, but I guess we’ll have to wait to see how this one turns out. Anyone ready to abolish software patents yet?