SubRingFM is a ring modulator. It also has two filters for shaping the sound, plus a sub-octave generator. The oscillator can be manipulated using FM.
The effect runs through a pre-filter to the ring modulator to a post-filter and then into a sub-octave generator. You can use the pre-filter to reduce the number of harmonics in the input signal and use the post-filter to shape the resulting tone. The ring modulator oscillator is an FM oscillator, so the resulting output can be made to contain a very complex set of frequencies. This can then be shaped using the post-filter to get a really wide range of sounds. The sub-octave generator is then applied.