Hot on the heels of this Commodore 64 synth browser emulator comes this web Theremin. Of course, clicking and dragging is a poor substitute for waving your hands and producing sound like magic, but it’s a fun time-waster nonetheless. As Waxy points out, there’s a Leap Motion version too, which I’d imagine more satisfyingly recreates the Theremin experience.
Those of us who don’t have one can watch Clara Rockmore play and feel bad for ourselves.