It is billed as the “world’s simplest electric train,” and it is almost certainly the case. Using only a battery, some strong magnets and some (bare) coiled copper wire, one can make the “train” travel numerous circuits through the copper “track,” until the battery is completely drained.
This caught my attention because it is a very clever twist on one of Michael Faraday’s original discoveries! Not electromagnetic induction, as I reflexively thought, but a homopolar motor. Below is an animation of such a motor that I whipped up in my office.