We have opened the Nimbus project on http://nimbus.dev.java.net/ to the public so you can go there and get the source or sign up to help out 
Posted on Mar 12, 2007
Nimbus project open to the public
Posted on Mar 9, 2007
Nimbus & Desktop Matters
I am sitting here at Desktop Matters conference which is fab. Now that Nimbus has been announced I can blog on it. Nimbus is a new Look and Feel designed by Sun which is going to be avilable in future versions of Solaris and there are a group of us making a pure Java implementation with the aim of making a modern cross platform look and feel. The aim is for Nimbus to support Java 1.5 and newer and based on Synth as far as possible.Nimbus is going to be a public opensource project at java.net and will be available very shortly. Ben Galbraith has some of the design mockups on his blog.As a taster here are a couple screenshots of SwingSet running Nimbus L&F.
