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Unfa says (I think same):
"ZynAddSuBFX is the most complex, powerfull and versatile software synthesizer I have ever seen. What's more it is free (libre) software with source code available. It might seem difficult to program at first, but thanks to a big set of patches shipped with it - new users can first explore what the synth can do, and then experiment with the knobs on their own.
Very good, reliable and powerfull softsynth"