Chair for people who have extremely tight hip flexor muscles. Lunge-type stretches are the best cure for this. But since such people are sitting at a desk most of the time, they need a chair that will help them do their stretches as they work.
The Lunge Chair is shaped kind of like a sawhorse. You
sit on it with one leg in front and one leg in back (like doing the "splits"). The front and back of the "sawhorse" become supports for your legs. The hip that you want to stretch should go in back. Adjust the angle of the leg supports to get the degree of stretch you want.
The top of the 'sawhorse" is the "seat" of the chair. It's just a little perch that the crotch rests on. I haven't worked out the modifications so that men could use it, but women could use it just fine.
The chair has no back rest; it doesn't need one. As you stretch, you tighten your abdominal muscles and tilt the top of your pelvis back. Your spine assumes the perfect curve and supports itself. (see Galen Cranz's "The Chair")
After one side is fully stretched, switch sides and stretch the other hip.
Search terms: Posture, lordosis, lumbar