Pretty out of tune, but funny. Stevie Wonder had a Harpejji, which uses an isomorphic pattern of frets and tapped strings. While not strictly a keyboard, this i

Pretty out of tune, but funny. Stevie Wonder had a Harpejji, which uses an isomorphic pattern of frets and tapped strings. While not strictly a keyboard, this instrument has been embraced by many keyboard players due to its consistent geometric patterns.