Acolyte

Presto has released Acolyte, a freeware monophonic virtual synthesizer in 32-bit VST plugin format for Windows, modeled after the Yamaha CS-01 hardware synth.
Acolyte copies most of Yamaha CS01’s functionality, including its VCO section with oscillator shape, PWM speed, glide, and pitch controls, the VCF section with cutoff, resonance, and modulation controls, as well as the EG and LFO sections. Much like its hardware counterpart, Acolyte is an extremely streamlined synthesizer that can serve as a great learning tool for users interested in understanding the basics of subtractive synthesis. It comes with all the features required for programming basic bass, lead, and SFX patches, yet doesn’t confuse newcomers with any of the advanced stuff.

http://presto.kohoutech.com