F2FM is the harmonicifier. designed for bass.
The name stands for "Filter to Frequency Modulation". It takes an oscillator, applies filter and resonance, and then uses that as the modulator on an operator. Add some distortion and you have some neat bass sounds.
check the demo (full disclosure, the pew pew sounds at 0:47 were sampled from who knows where, and the chords at 1:17 are synth1. everything else is F2FM