I have still not managed to put my hands on a Powerball yet, from what I have been told they are great fun and an excellent Christmas party gift as everyone wants a go. The idea is that it is a gyroscope spinning within a ball that you hold in your hand. You get the gyroscope going with a string then rotate your wrist to increase it's speed. As it spins the gyroscopic forces push and pull on your wrist muscles, the faster it goes the more it pulls and pushes. It has a built in digital display to record your performance and high scores.