Here’s an odd duck – the Gaus wheel. It seems very close to a scooter version of a unicycle, that is, without the seat or pedals. There’s a small castor wheel attached to the back and a platform like on a footbike. Voilà!
The learning curve would seem to be formidable, but videos show riders enjoying remarkable maneuverability. There’s a brake somewhere, but according to the manual [pdf] it’s mainly for slowing down. Like my old orange-crate scooter, you stop by jumping off.
Thanks to Will W. on the Yahoo! KickbikeUSA mail-list.