Although there are differing opinions regarding the health benefits of using a fit ball as a seat, a lot of people swear by it. That said, they don't always do it, because using a big inflated rubber ball as an office chair just makes them feel a little too silly. That's why Hungarian company Balance King has created its normal-looking Active Chair.
The top section of the chair (that part that you sit in) is joined to the base by a joint that allows it to tilt 360 degrees off its horizontal axis. As is the case with a fit ball, the idea is that instead of just passively resting your butt on it, you'll be constantly working your core muscles in order to maintain your balance.
Unlike a fit ball, however, it looks like a regular chair, and won't roll away on you when you're not using it. Also, the tilting feature can be temporarily disabled with a locking mechanism. This means that users can gradually wean themselves into full-time "active sitting" using the one chair, instead of having to switch between a regular chair and a fit ball.
Source: Balance King