SH-009 Monosynth is free VST plug-in for Windows PC.
SH-009 Monosynth is an emulated Roland SH-09(Roland does not endorse this plug-in of course). It is pretty close in functionality and sound to the hardware version. Highlights include a LFO modulator with random / sample-and-hold step voltage that can be used to modulate the oscillator, the filter, and the pulse width. It also includes an invert switch for the envelope, which can modulate the filter and pulse width, as well as the amplifier.