|Stirling Engine model (click to enlarge)|
To the point of this post, they also have a large number of Stirling Engine models. Above is a picture of one of their models -- click on it to see a larger view to examine its beautiful, retro-looking industrial design. Then go to the Bohm Stirling Engine section of their catalog and check out their full line. They also have videos there (they require written permission to use so I haven't embedded any -- it oddly fitting that a steam engine store wouldn't understand viral marketing on the internet).
Stirling Engines were popular during the 19th Century, but electric motors eventually replaced them. You can read more about them, and see more animated diagrams of their different configurations, at the Stirling Engine Wikipedia page.
The models at Ministeam are a bit pricey, but if you search Google you can find cheaper ones, although they don't look nearly as good as the Bohm Stirling Engine models.