HY-Plugins has released HY-Mono, a free to download monophonic synthesizer audio plug-in inspired by the Oberheim SEM.
There are two VCO units + Sub/Noise unit. Each VCO unit can generate saw/pulse waveform. Also, the LFO unit can generate sine waveform.
Frequency or Pulse width of the oscillator can be modulated by Envelope/LFO and with the Mixer knob, you can control oscillator volume in VCF panel.
HY-Mono Free synth plugin is available for free download in Windows 32/64-bit VST plugin format.
More Details/Download: HY-Mono