This Low Temparature Engines can run from the heat of your hand in a cool room.

A stirling Engine also called as a " Hot Air Engine ", uses an external heat or cool source to operate.
The engines work on a very basic priciple. When air or gas is heated it expands , conversely when cooled it contracts. Operation normally begines with a cup of boilling water placed underneath the engine. It can take as long as a minute to heat the lower plate enough for the engine to run.
The engine won't start by itself , but given a little push in the proper direction ( strong enough to coast the parts over for several cycles ) , the engine will take off and continue
running on its own. The speed may be increase as the engine heats up , and the slowly decrease as the water cools. Alternatively , it will run backwards when sitting on some ice.
This hobby engine can be a very good present for our friends & also family.

"http://www.youtube.com/watch?v=iEY-OGIcy6E"]YouTube - heat of hand low temperature Stirling Engine
"http://www.youtube.com/watch?v=mvX9C9ikIsg&feature=related"]YouTube - Ice & Hot Water Stirling Engine