Google Web Toolkit - Build AJAX apps in the Java language
I have no time to test it now intensivelly (as you can see, I have no time even for this Blog!!! ;) ) but ideas behind it (and demos on the official web site) seems to be very interesting and very very cool for Web-2.0-ready and agile-development process, using Java.
The interesting features? IT'S UNDER APACHE LICENSE!!! :D
If you want to get started with it, click here. Do not forget to come back here and leave a comment about it.