This desktop Stirling Engine from Sunnytech uses burning alcohol to create an external combustion process that will motor it all the way from China to your front door. Many who have purchased this model of "physics you can touch" note that it's quality is reflective of the price, but...check out that price. It gets the demo done pretty damn well for what it is and what it costs.
What this Stirling Engine is is a single flywheel unit with a glass tube sitting over a wicked vial. Fill with high-grade alcohol (e.g., ethyl) and light the wick to get the motor ready to roll in a minute or so. Once in action it will blaze along until the alcohol runs out (a few to a handful of minutes).
The Stirling Engine is set on an unpainted wood base Sunnytech probably chose because it's a super duper cheap material, but said they chose so you can "fly your imagination" and paint or stain it to your preference yourself.