One of the most appealing things about the KV331 Audio SynthMaster is its price: free (or very affordable, depending on which version you get). SynthMaster (Windows; $0-$99) is a semimodular software synthesizer and multi-effects plug-in available in VST, VSTi, RTAS, and standalone formats.
As a software synthesizer, the SynthMaster combines many different synthesis methods such as additive synthesis, subtractive synthesis, ring modulation, amplitude modulation, frequency/phase modulation, pulse width modulation, and waveshaping. As a multi-effects plug-in, it features an 8-band parametric EQ/filterbank; a 16-band vocoder; and stereo tremolo, chorus, delay, and reverb.
SynthMaster comes in two versions: free and standard ($99). The free version of SynthMaster is identical to the standard version except for a few limitations: 5-voice polyphony per plug-in, 2 plug-in instances per project, and 10-bit audio input resolution for the VST/RTAS/standalone versions. Download the free version here. The standard version of SynthMaster will be on sale from KV331 Audio in mid-December 2006.