re:tall ergonomic chairs, what is this type called?

[ondarkness]

Is there a name for it besides 'kneeling chair'?
I found some on ebay, but they seem to be too low.
I've seen taller ones in the past, but don't know what they are called.

 

[D1gger]

Found this item at Office Depot that looks like the same thing. They call it a body balance task chair.