Based on a concept first invented by Robert Sterling in 1816, this is a working engine that uses the warmth of a cup of coffee as its fuel. The fascinating twist is, this little Sterling engine is made entirely of paper, a $30 kit that you construct out of thick cardboard connected together with tiny wires. As you can see in the animation, its two tiny pistons move a crankshaft that turns the wheel.

The strangest thing about this minuscule motor is its ability to work with cold liquids, too, because it's the difference in temperature that makes the pistons pump. After you give the flywheel a push, the engine keeps on going under its own power for an hour or more. — Charlie White

Boing Boing, via Oh Gizmo!