This is a solar powered flag waver. It uses a solar cell from an old calculator to charge up an electrolytic capacitor. When the voltage across the capacitor reaches a trigger threshold the charge on the capacitor is released through an electric motor taken from an old video recorder waving a small flag.
I am not the original author of this circuit! Tinker Jim of instructables is! The original article is here: http://www.instructables.com/id/The-Easter-Solar-Engine. It is a really interesting article with lots of carefully researched information. The circuit seems to be nicely reliable - as Tinker Jim describes. It sits on a bookshelf and gradually converts photons into mechanical energy - constantly and gently surrendering to the passage of time.
The power of the flag waving motion is not overly dramatic, it has to be said. But the circuit is a nice example of the concentration of energy in a capacitor followed by its controlled release when a threshold is reached - which is the basis of a wide variety of different circuit types.
The circuit diagram is shown here for completeness - but visit Tinker Jim's excellent Instructable article for all the details.