Stirling Engine is a temperature powered motor.
The design of this engine was invented in 1816 by Robert Stirling as a safer alternative to steam engines. But it is never saw wide spread use because it was generally very heavy and required high temperatures. The principle of the engine is using a temperature difference in a cylinder and the air inside expands and contracts, moving a piston and a crank shaft in a rotary motion. The energy source can be any source of heat or cold, including solar or even an open flame.
This engine can run on the heat coming from your hand.
source: ThinkGeek