jo.Spectral Morph is a free Max for Live audio effect which is based on an FFT filter bank. Especially with its randomisable features, it's lots of fun to use and can be great to make a repetitive part sound more varied and interesting.
You can draw your own spectrum or have it randomly generated within a predefined range and density. In addition, the random spectrums can be re-triggered or morphed into each other. You can store 6 different presets and morph between them with the slider on the left. By filtering the signal it often becomes more quiet, so you should adjust the volume using the gain.
This way for heaps more Max for Live devices & tips.