How will you define a design that makes chairs that can be hung to a wall? ... I'll call it height space misery.

Jokes apart, there's actually a chair that falls flat when not in use and then you can hang it behind the door without wasting any space. It's called the Pick Chair
The chair features metal hinges on the sides that pivot to form a back, seat and base.
It will look good while hanging too as it can be engraved with designs ...so it becomes a beautiful piece for decoration at that time.
Available at Studio Dror