Picture of a BackApp from http://www.backapp.eu
Our distributor of office furniture is letting me try out one of these BackApp-chairs for a couple of days. It's supposed to train your back while you sit as you have to constantly keep your balance in it.
I've been using it for two days now and I can certainly feel my back having to work. And my stomach. And my hips. Precisely the parts of my body I really need to strengthen to avoid this mess, with a shifted upper body, in the future.
I can only sit for half an hour at a time and then I need to either stand or sit in my ordinary office chair for just as long or longer. The muscles get very tired from sitting in the BackApp-chair and one needs to transition in to being able to sit all days. And then when you're able to sit all day, you get to play with the resitance to make it harder and tougher.
To be honest, it would surprise me if we didn't get me one of these. I quite like it and I think it can do wonders for my back.