Based on my initial tests as well as reading a little deeper, I think what Sun is releasing under the GPL is the Java 7 source tree, a.k.a. Dolphin. This opens up several obvious projects. Take the Java 7 sources, rip out the new pieces, and create open source versions for Java 6, Java 5, and Java 1.4. Another obvious project is porting this to other platforms. If Apple doesn't GPL their VM, I'd definitely be interested in a third-party port.