All you heard and seen in your daily gym is just the forward moving treadmill. Take a look at this multi-directional treadmill (or omni-directional treadmill).

It seems a little dangerous since the guy is actually strap onto a rope from the top to prevent falling. But this would be a great practice and exercise. I usually get pretty bored on a treadmill and tends to run fast so that I could burn my calories fast and get over it. This may be a good alternative.

Updates: Wiki about Multi directional treadmill