The Active Chair by Alexander Christoff is an ergonomic chair that utilizizes an Anti-Burst gymnastic ball as the seat. 
Sitting on it your body is constantly making small adjustments with the postural muscles, abdominals, gluteals and leg muscles. It is “active sitting” rather than simply sitting upright in a chair with no movement.  Active sitting  promotes better posture,  increases cardiovascular efficiency, strengthens core and reduces stress.