This papercraft engine only needs to sit on a cup of hot coffee to drive its pistons. No, it's not the precious caffeine that drives the motion, but the Stirling engine design, in which the difference between alternating hot and cold gas pressure is harnessed for power.
Running for up to an hour on a boiling cup of coffee, the engine is said to work even better over cold surfaces, like ice. For $30, you get both a small piece of history and to make the world of paper your bitch. Not a bad deal at all. [product via boingboing]