Here is a unique musical device inspired by an abacus. The Abacusynth by Elias Jarzombek is pretty simple to use. You can adjust presence and modulate with a slide or spin. With a click on the side, you get to change waveform. Abacusynth is MIDI controllable. The below video shows it in action.
Pretty special, isn’t it? You can find out more about this amazing musical device here.