An orrery is mechanical device which attempts to illustrate the motions of planets, moons, and their parent star.
Despite heroic efforts over the centuries, there is no such thing as an "accurate" orrery - they, by practical neccesity, present distorted sizes and distances, and grossly oversimplify the complexity of real systems. For example, it's impractical mechanically to represent inclined elliptical orbits, so they are depicted as horizontal and circular.
But, while not telling the whole story, an orrery tells the broad outline of the story in a visually satisfying way, and this is hugely helpful to a human mind trying to grasp planetary motions. Plus, they're lovely to look at. I believe the world should have more orreries.
This project, currently in hiatus, aims to build a ceiling-mounted machine with a sun and about 3 orbiting planetary systems, each with orbiting moons. The design for a 3 moon planetary system with a turbulent "gas giant" planet (early version shown at right) is largely complete.
As is usually the case, this project turned out to be a lot more difficult and complex than expected. The eye is very sensitive to smoothness of slow motions, and it's not easy to achieve sublime planetary smoothness in a large, lightweight, belt-based mechanism. And the decision to make a "turbulent fluid planet" launched another major project.