Taking those electronic music playing greeting cards to a whole new level, Antonella Nonnis created a playable paper piano that she eventually hopes to turn into one of the awesomest pop-up books you've ever seen. The paper keys are all lined with a strip of copper foil that's wired to a series of megaohm resistors and an Arduino.
Using the same capacitive approach as your smartphone's display, the electronics can sense when and which key is being pressed to produce the appropriate synthesised tone. So instead of only playing Happy Birthday, one day a card could be used to play an entire concerto. [Antonella Nonnis via Creative Applications]