The Stirling engine is a Heat Engine - it is vastly different from the internal-combustion engine in your car.
A Stirling engine employs the Stirling cycle, which is completely different than the cycles used in
common internal-combustion engines.

The Stirling cycle uses an external heat source, which could be anything from burning gasoline to solar energy to the heat produced by decaying plants... or even a warm cup of coffee.

No combustion takes place inside the cylinders of the engine.
The gasses used inside a Stirling engine never leave the engine. There are no exhaust valves that vent high-pressure gasses, as in a gasoline or diesel engine... and there are no explosions taking place. Because of this, Stirling engines are very quiet.

 Invented by Robert Stirling in 1816, the Stirling engine has the potential to be much more efficient than a gasoline or diesel engine. But today, Stirling engines are used only in some very specialized applications, like in submarines or auxiliary power generators for yachts, where quiet operation is important.
Although there hasn't been a successful mass-market application for the Stirling engine, some very high-power inventors are working on it.

Stirling engines are generally very expensive - the two kits below are an affordable way to construct one of the most fascinating heat engines in existence.

Completed Eco Power Stirling Engine

The Eco Power Stirling Engine is our most affordable Stirling Engine kit.
Simply place the engine on a hot cup of water or coffee and it will run.
It's a great way to get into building Stirling engines without spending a fortune.
The included DVD instructional video makes the engine easy to assemble.
Precision CNC laser cut parts ensure the it will go together easily and run smoothly.
The most fun thing about this engine will be when your friends watch you run it and try to figure out how you got an engine to run on "water"!
Don't tell them it's really the heat, not the water, that makes it run!
If you'd like an engine that will run on smaller temperature differences (like ice) then you will want to buy the MM-5 engine (see kit below).

Eco Power Stirling Engine Kit: $50.00

Completed MM-5 Stirling Engine

The MM-5 Stirling Engine is a more robust and powerful engine kit.
You can power the MM-5 engine with a cup of steaming hot coffee or set it on a plate of ice chips (or a bowl of ice cream) to see it run in the opposite direction.
The MM-5 has been used for educational demonstrations from middle school science classes to United States Naval Academy thermodynamics classes.
This engine is also a favorite of engineers and techies all over the world!
If you need to give a gift to someone who loves technology this is guaranteed to make them happy. To assemble the MM-5 kit you only need to purchase some superglue and silicone sealant. You will also need a few common hand tools.
It's a pleasant two or three evening kit and a fun way to learn about Stirling engines. 
The MM-5 is an award winning science fair kit.
The MM-5 spins about 250 rpm on hot coffee or 100 rpm running on ice.

MM-5 Stirling Engine Kit: $120.00