SpaceTheremin is a virtual mouse-controlled theremin. Unlike a standard analog theremin, which typically has a sinewave oscillator and some basic vibrato, SpaceTheremin lets you choose from six different oscillator types (sine, square, triangle, sinc, saw, and pulse). The same waveforms can also be used for vibrato and modulation. It uses OpenAL for sound generation.
Use of the vibrato can result in some incredibly freaky and bizarre sounds. Set the vibrato depth (in percent) and adjust the vibrato frequency via the slider to hear the effects. A vibrato depth of 50% and a triangle waveform gives an interesting sound, for example.
Although the vibrato frequency ranges from 0.1 to 12.0 Hz in 0.1 Hz increments, checking the "modulation" box changes the range maximum to 8000. Moving this slider into the audible frequency range (20Hz and up) allows you to get strange two-oscillator frequency modulation sounds.