The Trebucard is a business card sized mini trebuchet. It is designed to fire jumbo paper clips and uses 16 pennies as a counter-weight. Unlike a traditional trebuchet the Trebucard uses the surface it is resting on as a pivot rather than being mounted on a frame.
This is a newer version of my business card that turns into a rubber band powered desktop catapult. It has been simplified and strengthened.
[Via Laughing Squid]