A simple somewhat Theremim using Beads/Processing.

theremim.pde

import beads.*;

AudioContext ac;
WavePlayer wp;
Gain g;
Glide gainGlide;
Glide frequencyGlide;

void setup()
{
	size(800, 600);

	ac = new AudioContext();
	
	gainGlide = new Glide(ac, 0.0, 50);
	frequencyGlide = new Glide(ac, 20, 50); //20 hz

	wp = new WavePlayer(ac, frequencyGlide, Buffer.SINE);

	g= new Gain(ac, 1, gainGlide);

	g.addInput(wp);
	ac.out.addInput(g);

	ac.start();
	background(0);

}

void draw()
{
	gainGlide.setValue(mouseX/ (float)width);
	frequencyGlide.setValue(mouseY);
}