Last year, I have made this ball balancing robot.It can stand on a ball stable by the balance system of itself.

There is only one connect point between the robot and the ground, so it is more flexible than the traditional wheeled robot. It can move to any directions without turn. For the traditional wheeled robot when its center of gravity is too high it may fall down, but by using this robot the problem will not exist. So the application on this robot can be applied to narrow, crowded and interference environment.
And this robot can be used in many areas, such as security robot, explorer robot and entertainment robot.
This is just a platform and don’t have any practical application on it. We can add all kinds of different function on it according to the situation. For instance, you can add the applications of obstacle avoidance, localization and control by network to realize the function of the document delivery with this robot in your office.
What’s more, there are two ways to control: with the handheld wireless remote control and with the Kinect. By using the Kinect, you can control the car with your body, that’s may have a lot of fun.
The software may include: WPF programing, Kinect SDK, AForge.NET, PID algorithm, Kalman filter algorithm, AVR MCU programing and STM32 MCU programing.
The hardware may include: Gyro sensor, Accelerometer, Geomagnetic sensor, Wireless module, WIFI module, Camera, Kinect, STM32 MCU, Atmega16 MCU, Brushed DC motor (with gear box), encoder, DC motor driver, Controller power supply and motor power supply.

You see the full article here on instructables.