One more effect, based on some tinkering I did while on holiday - I couldn't think of a good name, so it's called
Cross-Polyphonic FM (
main website,
audio demo with Hammer and Chord).
This is a MIDI-controlled frequency-modulator. You can add it after an existing synth, re-using the same MIDI notes to change the character of the sound, or have unrelated MIDI notes.
Multiple MIDI notes produces multiple modulation frequencies, but the notes aren't processed separately - they are added together to form a single modulation signal. This means that all the different notes interact, so open chords work well if you want it to sound tonal (similar to distortion).