Uncaged Ergonomics Wobble Stool
You know with a name like Wobble Stool they're gonna say it does everything but fall over. Uncaged Ergonomics has created this "healthier sitting environment" to encourage caloric output even while resting square on one's ass for 8 hours a day. The rounded base keeps the stool in constant flux, so your body is either braced for stability, or moving around with it. The perpetual Wooble Stool movement also makes it easier to lean, tilt, and bend to stretch, or pick up whatever Weapon of Cubicle Destruction just hit you and fell to the floor.
The Wobble Stool also has a tall adjustable height range, up to 33", for those who prefer standing at their desks, but occasionally want a leaning break. A triangular saddle with rounded edges is extra-cushioned for comfort and adaptability to a wide (literally) range of buttocks. And, of course, the stool's rubberized bottom is both non-skid and weighted so Wobble always, always comes back to its full upright position.