The $29.99 all-metal desktop Stirling engine kit is one of the simplest. It can be assembled in 15 minutes and is recommended for ages 14 and up. Also for $29.99 is the Exploring Kid Steam Engine Kit.

If you're an automotive enthusiast, you probably love supercars and other rare or unique models. But few of us can afford to actually buy (and run) such ultra-exclusive über-rides. The everyperson's ...