Yesterday was a landmark that plenty of us have been working towards for nearly a decade. As MR and I have been indicating for a while now, the remaining obstacles to a fully compatible and Free implementation of Java SE have all been removed by efforts like renegotiating the terms for the source of Java 2D and various community members (Sun and others) re-implementing some of the other code.
But the proof is in the fruit of the process, and yesterday it was confirmed that the implementation of OpenJDK 6 that the Fedora community has packaged does indeed pass the TCK. This is a huge achievement for everyone who has been involved - the Fedora team that Rich mentions in that last link, the team that MR leads at Sun, the team that I lead, plus the many, many people who have worked for a Free Java for so many years.
Some may fear, as Fabrizio does, that this (and the many GNU/Linux, OpenSolaris and BSD packages that will follow) will lead to such a diverse set of Java implementations that "write once, run everywhere" is doomed. I don't agree.
What made Java so compatible, in my view, was the fact that almost all versions found in the wild were built with Sun's class libraries even if they used a different VM. With Sun opening the reference implementation and then the community taking it on and embracing it, we now have that same basic code-base at the root of Free implementations everywhere. And we now have the benefits of community diversity to ensure many eyes are making bugs shallow and that innovation is accelerated.
Free, compatible Java everywhere. That's exactly what we all wanted, and we have it at last.