ZynAddSubFX is an open source software synthesizer for Linux, Mac OS X and Microsoft Windows.
For sound generation it has three hybrid synth engines that combine additive, subtractive, Fourier and other synthesis methods. No external samples are used to produce the sound; everything is done by synthesis. The synthesizer has effects like: reverberation, echo, chorus, distortion, equalizer and others, and supports microtonal tunings. The author of ZynAddSubFX is a Romanian programmer, Paul Nasca. The work started by March 2002 and the first public release was version 1.0.0 in September 2002.... More Info »
A VST port implementation is available: it's still in beta development, but has been tested with hosts such as VSTHost, EnergyXT 1.41, Cubase and Reaper.