Oh, nothing fancy, just an analog square wave synthesizer...
(This unit is like OKAY #1 but in black and with twelve octave selection instead of three.)
Unit: 2 Version: 1.0.1
External controls: 13 keys, octave selector, volume knob + on/off switch
Internal controls: 13 trim potentiometers for tuning notes (hidden beneath respective key overlays)
Dimensions: 7.5"x 4" x 2"
IC Chips: LM555, CD4040, LM386