Stirling Engines, Art
This is interesting: A Stirling Engine that you can run on your kitchen table, that looks like a piece of art. I'm not sure why, but I really like the looks of the engine in the picture. It looks functional, but it's still pleasing to look at. A lot of cool mechanical things are like that, I guess. If I had a nice office, I would want one of these on the bookshelf to play with. (Then, I suppose I'd spend lots of time sitting in my nice office playing with it, neglect my work, get in trouble, and possibly lose access to the nice office and have to sell the Stirling engine to buy food. Life is full of difficult issues like this!)
For those unfamiliar with Stirling Engines, they're engines that convert a difference in temperature between two points directly into mechanical energy by repeatedly heating and cooling a fixed volume of gas. In the case of the one pictured above, the "hot" side of the engine is the little metal burner at the base heating the thing sticking out of the other thing. The "cool" side is apparently the ambient temperature of the room the engine's running in. The rev. Robert Stirling invented the engine in 1816 after several people in his parish were killed by exploding steam engines. Unfortunately at the time, metallurgy wasn't to a point where a Stirling engine could be built that would last very long. Materials are better now, and Stirling engines are appearing with more frequency.
Because of the facts that a) They don't produce much useful power for their size, b) they can run on anything that generates heat (including the palm of your hand, in one case), and c) are almost completely safe, you typically find them marketed as toys.
I've always thought it would be cool to have a Stirling-powered car, so I could drive back and forth to/from work for a week fueled by nothing but body heat and the by-products of my digestion of Mexican food. The problem is that (as I mentioned above) Stirling engines don't generate much power for their size, and the concept of a "throttle" involves reconfiguring the engine mechanically, not just metering the amount of fuel. So, it wouldn't make a good car engine.
Famed inventor Dean Kamen (inventor of a wheelchair that climbs stairs and the gay-looking-but-interesting Segway) has been developing a Stirling engine design to power portable generators. These could (and ostensibly, would) be used in third-world villages to generate power. The general idea is that villages full of starving Ethopians will be able to burn grass and dirt to fuel the generators, which will generate electricity, which will power the Ethopians' laptops, so they can get on the internet, and use Google Maps to locate the nearest Pizza Hut. Wish I'd thought of that!