Typical digital touchscreen pianos I've seen mimic a physical keyboard, i.e. a series of vertical keys rising in pitch from left to right.
My question is: are there alternative digital touchscreen keyboards that use slightly or radically different interfaces?
(For a loose analogy of my thinking behind this question, think of the QWERTY versus Dvorak computer keyboard layouts. QWERTY is based on mechanical typewriters which arranged keys to have common sequences of letters separated, to minimize mechanical jams. Dvorak gets rid of that requirement and optimizes for keying speed. Similarly, I'm wondering if there are more "optimal" ways of inputing notes/chords in a digital touch-screen setting than the standard left-to-right piano layout.)