The Prophet VS was the only digital synth that Sequential Circuits ever built. It was a bit like a grittier Korg Wavestation (some the team who built it joined Korg when SC went bust), with that lush-but-slightly-cheesy '80s sound. A new VST version of the notoriously hard-to-repair Prophet VS is now available. It's called Vector Sector and it was developed by Joshua Jeffe, who was part of the original Prophet VS team at Sequential, and went on to build the EMU Proteus 1. There's a great story about the invention and birth of the VS here, and some VS samples from Hollow Sun here.