There are a variety of boards available that have a magnet on a rod (to be held like a pencil), and little metal balls under a perspex cover. See photo.
The object is the move the balls using the rod with the magnet on the end. In order to move the balls along a path requires a person to plan movements. The paths include many corners. It's a bit like a maze. They come in different levels of difficulty and different appeals for children. There can also be a challenge of coordinating vision and developing the use of vision, especially as the ball cannot always be seen clearly, depending on the angle of the rod being held.
These boards are valuable in teaching a child to plan their fine motor movements. They need to be moving the ball and at the same time, using vision coordinated with thinking, to plan ahead. Great for learning to integrate these skills. These boards will develop skills that will be useful in printing letters.