https://femurdesign.com/theremin/

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“Theremin is a free online synth instrument that makes an array of different sounds. Play it by dragging the cursor or use multiple fingers to fiddle with waveforms, and experiment with the delay, feedback and scuzz sliders.

In the new app version (available for iPhone / iPad and Desktop), you can make layers, record, loop and download creations. The app allows use offline to play live at shows, in the studio or anywhere.”