Here is a cool open source robot that can keep its balance on a regular soccer ball. The Ballbot features an under-actuated system with a single-point contact. It comes with app connectivity, so you can adjust various parameters.
The ballbot has an aluminum alloy base. It has a 0.96inch OLED display and uses a 24V 5AH lithium battery. It can move and rotate in all directions when on a ball.