Spotted in the MAKE Flickr pool, this homemade contraption from user Whymcycles who, besides having my favorite UID ever, has this to say about his creation:

Made from an 8 foot..96″..pair of power line spool hoops, sized down and painstakingly re-arc-ed back to more or less circular 84″, and crossbars of electrical conduit. Also with 4 handholds made from Schwinn Varsity drop bars…and foot straps of old car seat belts. We’ll see if practice, persistence and careful study of YouTube European footage..will allow me to learn some of the art of Wheel Gymnastics.

The device itself is called a “Rhönrad,” “gymnastics wheel,” or “German wheel,” and is apparently the basis of an entire sport in Germany.