StereoTool is a Max for Live audio effect which gives a broad range of controls over your stereo signal. It's a very useful tool when mastering.
Mid/side and left/right can individually processed, muted, delayed and the gain adjusted. Both mid/side and left/right can also be bypassed. For mid and side the phasing can be added, for left and right the panning.
This way for heaps more Max for Live devices & tips.