The Aspiral Clock ($540) is a self-spinning timepiece, whose movement drives a ball along a spiral ledge until it reaches the center. The observer can tell the time by looking at the position of the ball. If it’s at the center point between 2 and 3, for instance, then it’s 2:30. Once the ball reaches the center of the clock, it drops into a hole and comes out of the same opening where it originated.
London based Aspiral Clocks offer multiple designs on their site.