The crazy people at Waterloo Labs developed a system to play the computer game Half-Life, a First Person Shooter, using accelerometers, drywall and a integrally suppressed Ruger MKIII.

Looks like a lot of fun!

A parts list and computer code to build a similar system can be found at Waterloo Labs.

Many thanks to Antonio for the link.

UPDATE: Nookyon points out in the comments that the game appears to be a flash based “remake” of Half Life, not the original.