One of the main obstacles during typing on flat keyboard is deficiency of tactile feedback. So my idea is that each key vibrates with different amplitude or frequency when it pressed and when not. Space between keys not vibrating at all. G and H keys on qwerty vibrate differently from other keys (or just have usual marks). It will allow to create slim keyboards without moving parts and with tactile feedback. Also, this idea can be used in desktop keyboards with different rows of keys...