I think I and quite a few others have had this idea before, but some crazy Russians have actually built a 10-foot, stationary hamster ball for humans that translates movement to on-screen action.
Given the oft-hilarious Russian inventors, their equally staid and awkward American partner and the fact that this is on Vice Magazine's video site, a part of me thinks this might be a joke, but it actually looks like they've gotten the thing to work. It's essentially one of those giant American Gladiator balls, but placed on a stand equipped with wheels, so whoever's inside can run in any direction. The users are equipped with goggles and what looks like a plastic laser gun for the first-person shooter demo, and the game picks up movement pretty nicely. We imagine it'd be tougher than they think to change direction on a dime, and of course not that many people have room for a 10-foot metal ball in their family room, but it's worth a look. Best line: "It really is a locomotion simulator. And just to define locomotion, it doesn't have anything to do with trains [dude does his best to hold back a vigorous guffaw at this pun] but with the movement of people." [VBS.tv]