MaKey MaKey: Hook up random stuff and use it as a keyboard
Wow. MaKey MaKey is an easy-to-use kit that lets you hook up anything (well, anything that can conduct a bit of electricity) to your computer using alligator keys and cables, and then hit these random objects as computer keys or mouse buttons. The power is yours to do this will cost you just US$49.99. If you understand your geek stuff, the MaKey MaKey is really a printed circuit board with an ATMega32u4 microcontroller running Arduino Leonardo firmware that uses the Human Interface Device (HID) protocol to communicate with your computer and send keypresses, mouse clicks, and mouse movements to it.