Ball shaped (Spherical) robots

Would you share with us if you know any URL for ball shaped (sphere)
robot?
Any design/implementation details/ideas how they work?

URL List Ball Shaped Robots:
(1) Rotundus
    http://www.rotundus.se
(2) Mobile Ball-Shaped Robot
    http://www.automation.hut.fi/research/robotics/ball/ballrob.htm
(3) Roball
    http://www.gel.usherbrooke.ca/laborius/projects/Roball/index.html
    Roball-An Autonomous Toy-Rolling Robot
    http://www.gel.usherbrooke.ca/laborius/papers/WIRE00.pdf
(4) RoboMaid (***)
    http://www.robomaid.com
(5)