Nocturna is a free wavetable FM synth VST instrument for Microsoft Windows. Including 2 wavetable Oscillators, dual LFOs, and Sub Oscillators It allows you to get deep into sound design. Included is a large sound Library with a 64 preset library, future expansions and dozens of waveforms.
Crystal is a free semi-modular software synthesizer VST instrument featuring both subtractive synthesis and frequency modulation (FM) synthesis.
Xen-FMTS 2 is a free 4 Operator FM Synthesis VST instrument with a specialized set of features for computer musicians interested in exploring the vast expressive possibilities of making music with alternative intonation systems. It is a freeware 32-bit plugin instrument for Windows that includes 115 patches, 55 microtunings and 56 partials files.
Synthipop is a free frequency Modulation synth instrument with 8 fuzzy, gnarly, skanky presets, all re-writeable. Use this synth to put some gin in your tonic.
The Wollo FMERA combines FM style sounds with a wave player. Included is one dedicated single stereo female voice sample, which will be triggered together with the fm sound. With onboard effect processors.
Uniwave is a free VST synthesizer instrument based on a substractive architecture, Uniwave have also some FM capababilities. A few unusual controls permiting to tweak and bend your own sound.