Quake has been ported to a wide variety of platforms, but none quite like this one. Programmer Pekka Väänänen managed to get the game running on an analog oscilloscope. Check it out:
Väänänen's code transforms the game's geometry into a stream of X/Y coordinates that's fed to the 'scope through a USB sound card. The graphics aren't great, but the latency is apparently low enough to "play comfortably with a keyboard and mouse." Pretty cool.