Eon's ICube uses a combination of stereo projectors, stereoscopic glasses, motion tracking position trackers, and 3-6 walls that wrap scenes around their corners to give users the illusion of a "complete sense of presence" in a displayed virtual world.

The system also supports peripherals like force feedback devices, a gesture dataglove, and a wireless wand that looks like a power drill or a Romulan disruptor. Multiple users can walk around the setup at the same time, provided they all have their own pair of glasses. Here's a recent video of IDEO Labs taking the ICube for a spin (and almost falling over while trying it out):

[via Technabob]