Project Looking Glass is a 3D desktop environment. It is java-based and so platform independant (So it can run on Windows/Linux et al). Sponsored by Sun Microsystems.
Personally, I havn't tried this Desktop environment, but it fascinates me. May be some day.
Check it out here
The sad thing is that, I couldn't find a decent screenshot on their site. So here are some screenshots I got through google
The project is still open for active development, so there might be some opportunities for those desperately-searching-for-prob-def BEs.
12 hours ago