Sun has an OS-neutral, Java based 3D interface extension for your OS, available for free. It works as an overlay to your current OS and allows you to rotate windows in 3D space on the desktop.
Beside offering 3D, rotatable views of open windows, you can organize the windows on their side for a bookshelf type of view, or move to a new virtual window to the left or right to give you multiple virtual desktops at once.
The open source project has been ongoing since 2003 with downloads available since 2004. There is an update as recently as 8/16/2006 so it is still ongoing. They are also actively inviting others to join the project to further explore the possibilities of the technology. Currently downloads are available for Windows, Solaris and Linux.
