MangledVerb first appeared as an algorithm in the rackmount Eventide Eclipse effects units. It then migrated to the H9 guitar pedal, and is now available as a self-contained plug-in supporting all the usual formats.
The design aim with the True Overdrive 1 was to emulate the way valve circuitry behaves, so that the sound cleans up very naturally as you back off the guitar volume control or play quieter.