This has been around for a while, but since I just recently found it, I figured I’d add it to the growing collection of the other "jet" stuff (here) – the Jet Go-Kart.
The article says that this was orginally used as a starter for the main jet when ground services were not available, so the builders had a lot to do in order to make it possible to run more than a few seconds. What I like about it is that it is not only fast, it LOOKS fast!
(H/T: Ohgizmo)