| Also a simple toy; I don't know whether it's still in production, but I had one as a little girl. I never took it apart, but recalling the sounds I heard while using it, probably the main components were two pieces of plastic and a bunch of ball bearings.
Basically, a Sit 'n Spin is a round device with a mobile platform on the bottom and a circle upon a pole sticking out of the top. One sits on the platform, preferably with one's legs wrapped around the rest of it, and tries to turn the circle on top, causing the platform to start turning. One does this until bored or dizzy; I usually got dizzy first, to the point that when I finally stopped spinning on the thing, I always said to the room, "Don't walk." (Hey, I was only three or four at the time)... | 
