SE PolyMod is a virtual analog synth that sounds better than anything in the free domain I have heard so far. The two oscillators (actually three counting the sub osc) combined with the noise generator and the ring modulator with EQed inputs (which is a brilliant feature!) give plenty options for sound generation. Nearly any type of modulation is possible, e.g. phase modulation, frequency modulation, ring modulation -- as long as you do not wish to modulate the modulation depth (as FM synths can usually do). PolyMod is NOT an FM synthesiser, and it never claimed to be.
The filters are super flexible thanks to various models that can be selected, and thanks to flexible routing. They are even kind of dry/wet-able. And as everything in this synth: they sound good.
Do not be fooled by simple ADSR envelopes. The env-times can be controlled by velocity and key follow. And they have a number of slope shapes available. Super useful for sound design! Not sure if the odd behaviour of the filter envelope depth knob (v1.07) is a bug or a feature. Regardless, I haven't met a case where I could not work around and get what I wanted using another envelope.
Also, as the developer states on his website, this synth is not made for synthesis beginners. Even for experienced folks it needs some time and luck to find all the features you can get from this synth (hint: click on labels!).
The synth can be a bit heavy on CPU. But given the sound quality I would say it is a pretty good tradeoff.
5/5 stars for top quality sound and flexibility despite the minor usability flaws I mentioned above.