In addition to causes like stopping malaria and promoting organ donation, Bill Gates is trying to wean the world off oil in his spare time.

Bill is listed as one of ten co-inventors of a new type of "electromagnetic engine," in a patent application filed with the U.S. government today.

That doesn't mean Bill actually invented the thing himself. Inventors routinely list others as co-creators, and another co-filer is former Microsoft (MSFT) CTO Nathan Myhrvold, Techflash notes.

So just what is it? Well there's diagrams, and the abstract says "a converter converts mechanical energy of a piston to and from electrical energy during each piston cycle," followed by a lot of notes that are bewildering to this layman.

If anyone can make sense of the filing, let us know what's what in the comments. But "electromagnetic engine" automatically makes us think of electric cars, a burgeoning industry. (See The Complete Guide To Electric Cars.)