Before the electric keyboard came out you had these:
A primitive version that responded by touching the knobs.
By pushing hard or soft on the knobs, you can change the pitch or tone of the sound coming out of it.
(or select different knob combinations with your fingers, using two or more fingers)
This version has been based on the macbook in technical design. (alu-housing) Two blocks of wood with cut out space in the middle nicely finished with a bit of paint. Removable battery compartment, led indicator and volume control make it the perfect old-school instrument from the old days.