Zimbelstern is a "stop" or a setting on a pipe organ that produces sounds from a set of high-pitched, untuned (or tuned) bells. The name comes from the fact that the bells are rung (or sounded) by a rotating wheel that is often in the shape of a star, and it sounds like little cymbals being rung by a star. The revolving star was placed towards the top of the organ case (in view of the listeners) and a wind-blown driving-wheel behind the case was attached to the set of bells. Modern versions are rotated by electric motors.
This "stop" or setting is known as a "toy stop" because it is considered to be a toy or novelty sound (sound effect), not a real musical sound. It is found mostly on baroque and classical northern European organs (especially German and Dutch) and was popular from around 1490 to 1790. The bells were originally untuned but by around 1700, they began to add tunedbells.