Dan sez, "Astromedia is a German science gizmo company that specializes in die-cut cardboard widgets: astrolabes, sextants, telescopes, etc. But this new one takes the biscuit -- a Stirling engine that works on the heat from a cup of coffee. Apparently, if you set it on a frozen compress ("Setzen Sie ihn auf eine Kaltkompresse..."), it runs for hours." Link (Thanks, Dan!)

Update: Pschemp prepared this translation for us!

The Stirling Engine
Runs on a cup of coffee or an ice pack

The revolutionary concept for this hot-air engine was discovered in 1816 by the Scottish minister Robert Stirling and has been updated for today. The principle is as ingenious as it is simple: In a sealed cylinder, heated from the underside, a piston pushes the enclosed air back and forth between the hot and the cold side. The air therefore expands out and compress together every cycle and that movement is converted via a moving piston and crankshaft into rotary motion.

As an energy source, any type of warmth or cooling that produces a temperature differential can be used, from an open fire to solar energy or any other unused source of heat or cold.

Set this fully functional Stirling engine on a cup with boiling hot coffee (Tea or water also works of course) - give the flywheel a small push to the left - and the apparatus begins simply to pump up and down - for up to an hour!

This isn't everything it can do: Set it on an ice pack or ice cubes from the freezer and turn the flywheel to the right and it will also pump up and down for an even longer time.

(Caption:It is really a marvel)

Kit made from sturdy punched cardboard with gold stamping, complete with all accessories including laser cut aluminium plates, low-friction plastic axle bearings and spring steel bent wire.

Height 16.5 cm, width and depth 12.6 cm.