Quilcom Adder is a free VST Synthesizer Instrument. There are 16 sine wave partial strips. Each one has its own envelope with velocity response and amplitude tracking of the pitch and can be set to any pitch ratio. Each partial can be panned left to right to give increased stereo richness. There is a single FM bus fed by 2 FM modulator synths and the level of FM can be adjusted for each partial.
On the right side of the GUI you can set MIDI-related stuff and there are 3 LFOs. One is dedicated to the MIDI keyboard’s mod wheel for introducing vibrato, the FM LFO controls the overall pitch modulation independently and the AM LFO is sent to the partials and each partial can have the AM level set.
At the bottom of the partial racks there are 2 basic synthesiser strips which can be used to provide simple filtered waveforms or noise and their outputs can be panned. The idea is that you can get a basic sound with these synths and then use the partials to modify and extend the sound, should you wish to work that way.
Since there are so many sound generating possibilities it’s easy to lose track of what is contributing to the sound so you’ll find that each generator in the rack has a mute switch to toggle its contribution on and off.
Finally, the bottom row features a pre-routed effects chain, the signal flow going from left to right and each one can be enabled or disabled individually.
Try a few presets and see what you think. Beware the CPU use is high, due to everything going on inside, so on less capable systems you may have to freeze the track or render it down if using multiple VSTs in your DAW.