For Bad Ideas I built a computer controlled anti-mouse sentry turret. The turret uses a video feed from a webcam and a slightly modified version of the Project Sentry Gun Processing code to track mouse-sized objects that move across the camera's field of view. It fires at the objects using a hacked electric airsoft gun on a pan/tilt servo platform.
After the winter break, I brought a projector I got from old high school's recycling pile back to my dorm with me. I made a screen for the projector from some blackout fabric, and motorized the raising and lowering of the screen with a small gear motor and some other parts I found.
PocketBoard is a 14.5" long skateboard designed to be the opposite of my electric scooter: It is a small, simple and reliable vehicle for going short distances quickly. At roughly 5% the weight of the scooter and some small fraction of the volume, I can easily store it in a backpack or even my laptop bag when I'm not riding it. It has a solid oak deck with inlayed aluminum plates, and (what I assume to be) standard skateboard trucks, along with some soft 60mm diameter wheels.
PocketBoard V2 keeps the same shape and footprint, but has an aluminum deck made from the side panel of a PowerMac G5 case.
PocketBoard's rather short build thread can be found here.