The Fit Disc can be used for balance and core strengthening (abdominal and lower back) exercises. Enhances the posture as well.
I find the balance discs a great portable tool to help with a workout.
Some exercises that can be done using the Fit Disc:

-Standing single leg balance, core balance sit
-Sitting on the disc to do crunches and other ab exercises
-Standing on the disc while using dumbbells for arm strengthening
-Standing on the disc while doing squats
-Use the disc while doing lunges, step ups, push ups, planks

I got this to do proprioception exercises as part of my knee rehab. It's a lot like the one my PT gym has. The only problem I've had with it is that you can't adjust the inflation and it's a little under-inflated for me. The main exercise I do on it is to stand on it with one foot - but if I try to do it without shoes on (which I'd prefer) my foot bottoms out and ends up partly resting on the floor instead of on the cushion. My feet are women's size 7.5. (It works if I just wear flip flops.) Anyway, the price was decent and it's pretty good, just not adjustable.

My sister purchased a cushion similar to this one from her physical therapist for about $50. It is the best thing I have used for sitting on hard bleacher seats during sporting events. (Hers was similar to: Fitball Seating Disc Balance Cushion)

I didn't want to pay $50, so when I found this at Ross for under $10, it became mine. It works as well as her $50 cushion and I am delighted that I didn't have to pay the higher price.

For the reviewers who are not able to use this in the traditional way, try sitting on it the next time you go to a football or basketball game.

I have been suffering from leg pain for over 15 years, due to a sports injury. The problem may be a damaged tendon or ligament high up on my left leg. I have tried all kinds of chairs and pads. I have even used expensive jell cushions. Nothing seems to work. This product goes in the pile of do-nothings. In fact, my pain increased using it. Granted, I may not be using it as it is designed, as an excercise tool. Never-the-less, it is not for me or perhaps others who suffer from similar leg pain. I do a lot of work on the computer, hence the need for a comfortable seat.

this balance trainer is perfect. it's a very nice, thick plastic just like the ones you see at the gym. so many exercises to do!