Kneeling chairs or stools were designed in Sweden back in the 70's and apparently enable you to sit properly for hours with a straight back. They usually have no back support to ensure that you have to sit up straight. You put your shins and knees on knee pads putting your behind on the seat of the chair. Your body weight is distributed between your shins and your bottom. The design eases your hips and aligns your back, shoulders and neck and is supposed to prevent back pain.
They look a bit odd and may take some getting used to but they can be great. The original designs were quite simple and often had minimal adjustments so that if you were very short or very tall they could be quite uncomfortable. They were also often quite low on the ground so they weren't really practical for the office. I should know as I used to have one in the early 80's. It was more of a kneeling stool, low on the ground and you knelt on the two side pieces and sat on the bit that jutted up from the middle. Although it felt quite awkward it was great for watching TV and certainly helped me to sit up straight. Not to mention it was a great talking piece with all my friends!
The Computer Chair Version
If you are using a typical off the peg home office furniture system you need your chair to be at the right height for the desk and to be able to move it around. Some kneeling chairs are now designed so that you can do this. The top of the range models not only allow you to adjust the height of the chair but you can also adjust the knee/bottom ratio. This means that whether you have shorter or longer legs the chair will still fit you. With a five star base and caster wheels you can easily move around your office.
The memory foam pads also mold to your body so that the chair almost becomes part of you. Some of these types of chairs also have backs, therefore looking more 'normal' while still giving you the benefits of a kneeling chair. Others are made of wood and are made with runners instead of a more normal chair base. They end up looking a bit like a cross between a stool and a rocking chair.
This is certainly a case where you need to try before you buy as not everyone finds it easy to adjust to this type of ergonomic seating. However if you suffer from lower back pain then they are certainly an option worth considering.
At the lower end of the market you can buy a kneeling chair for less than $150 but if you want a top of the range original style Balans chair with rockers you can pay anything from $400 for a simple one to over $1000 for one with a back. A more conventional looking Balans kneeling office chair on a five star base without a back will cost you around $600 depending on the model and fabric used.