This one almost made it as a transportation entry. Almost. There's nothing inherently nuts about using compressed air as a power source, and there are several companies working on exactly that.
But right after they make their case -- the makers of this video (I have no idea who actually made it) present their vision of the potential -- putting an air-powered compressor on board, to compress the air for the car, thus presenting the potential for a perfect closed circle, yada yada yada.
And then -- just when you're thinking, no, they CAN'T be proposing a perpetual motion machine, they actually call it a perpetual motion machine.
Anyway, see for yourself. Not a bad video, up to where they take a π/2 turn into left field. Which is what makes the sudden turn so surreal.