A Video Game Made of Cardboard
Here's a video game (a sort of ultra-simplified Super Mario Bros) made using paper, some motorized rollers, a speaker, a knob, a cardboard box, and an intriguing little circuit board thingy called a Teagueduino. It's a little hard to explain what this is and why it's awesome, so just watch the video -- and stick around for the second half, in which the creators take it apart to show you how it works. Fun, but probably not much replayability.
Video Game in a Box from adam kumpf on Vimeo.
If you want your own Teagueduino, they're hosting a Kickstarter project. For $160 you get your own electronics kit so you can make stuff like this! The source code for this program is available, along with configuration instructions.