Project Looking Glass
2003 – Sun Microsystems rolls out an experimental 3D Desktop Environment called “Project Looking Glass.” This 3D environment, available for Linux, Windows and Solaris, never really caught on itself, but the impact it’s had on newer environments is noticeable. For example, reversible windows – the ability to flip a window around and have additional controls (notes, settings, etc.) on the back. There are other examples, like the Windows feature where you can scroll through all open windows in a sorta-3D view, or the glassy, 3D-ish looking Dock on MacOS X.
Fun Diversion: This wasn't the only attempt at 3D desktop interfaces. Some less successful attempts can be found at the Croquet Project and Microsoft's TaskGallery.