Vivaldi and Ganymed are two new FM VSTi's by Stefan Jeworowski, available for both Windows and MacOS, and both are free!

Vivaldi's key features:

• 4 x 2 Operator FM Synthesis.
• Up to 32 voices polyphony adjustable from the UI, including a smart & smooth voice stealing algorithm.
• Up to 4 parts per note for voice layering, including support for velocity and key window.
• Sample precise support for all usual MIDI controllers (volume, expression, panpot, pitch bend, ...).
• Support for all sample rates (22k, 44k, 48k, 96k, ...).
• True 32bit floating point signal processing on per-sample-basis (no down scaling!).

Ganymed's key features:

• 3 Operator FM Synthesis.
• Up to 32 voices polyphony adjustable from the UI, including a smart & smooth voice stealing algorithm.
• Many modulation sources: 3 ENVs, 3 LFOs, 6 Mod-Adders, 2 MIDI sources, key, velocity, 4 SEQ sources.
• Rich modulation capabilities: Every modulation source can be routed to almost every sound parameter.
• Built-in 4-track pattern sequencer for complex modulation sequences (syncable to your host sequencer!).
• Sample precise support for all usual MIDI controllers (volume, expression, panpot, pitch bend, ...).
• Support for all sample rates (22k, 44k, 48k, 96k, ...).
• True 32bit floating point signal processing on per-sample-basis (no down scaling!).