The Soulseat (pictured above) that we looked at here is an interesting, relatively simple alternative design for an office chair that allows you to sit in a variety of positions. I'd never seen anything quite like it, but have just learned they're not alone in this market. Competitor Pipersong offers this "Meditation Chair:"
Though the functionality conferred by both chairs is similar, Pipersong's design is rather different. In addition to featuring a backrest, their kidney-shaped lower support swivels around the central axis, providing a bit more flexibility.
From an aesthetic perspective I prefer the look of the Soulseat; visually it speaks of refinement, of a concept that has been winnowed down to its essentials. In contrast the Pipersong and its seven wheels look a bit clunky to me. But I can't argue that it isn't form-follows-function.
Aesthetics aside, the big differentiator to potential buyers may be price. The Soulseat is north of $1,200, while the Pipersong is just $330.