For my son's 5th birthday party I created a game. It's a 2 player cooperative fps space shooter played in our own solar system. It was targeted for Linux but with a little work it could be ported to any OS that Irrlicht supports.
To make it a bit more unique, I built a physical spaceship with a pilot's seat and a turret mounted cannon, for the two players. The pilot controls the spaceship with a mounted joystick (the trigger controls guided missiles), and the gunner shoots directly at the projection screen.
Shots on screen are picked up by a regular NTSC CCD camera and evaluated by a circuit that I built which looks for a laser dot on screen. The laser is very low power (eye safe) IR, and there's an IR interference filter on the camera so it works just fine under flourescent lights (I've got CFLs in the basement where this is set up). My circuit reports pixels on screen above a threshold set by a pot on the circuit. Turns out this works pretty well.
The party was a big success- the kids had a great time playing it. I plan to release build plans and sourcecode for everything (provided somebody is interested) but I've got a few bugs to fix first.
Anyway- here's a video of my boys in the spaceship:
And here's one of the game (just a video of the screen)
I set up a blog while I was developing, but did a poor job of maintaining it. My upload rate is abysmal, so have some patience if you check it out:
Finally, I'd like to thank all the folks here who helped me during the main development.