Simple spinning top that once you plug in and spin it, will continue spinning until you unplug it. Powered over USB.
Todo: Recreate circuit diagram and post photo here. Its a simple circuit that charges a capacitor until it detects the magnet over the coil, and then uses that built up charge in the capacitor to spin the top just a little bit more, helping it maintain its speed indefinitely as long as it continues to stay plugged in.