Note Displacer is a free Max for Live MIDI effect by J Garcia, that randomly transposes incoming MIDI notes by predetermined intervals. Melodies or chords that are very simple and can become boring after a while thus can be varied in interesting ways without effort.
The probability of the effect actually doing anything at all can be set as a percentage. Just as whether notes should be transposed up or down. Also notes outside of an area can be sent through unchanged.
This way for heaps more Max for Live devices & tips.