When Ableton first announced Max for Live I knew this plugin / add on would be a game changer. I had to get a copy as soon as possible.
For the uninitiated max for live basically lets you use a simple graphical programming language, called max/msp within Ableton Live. This lets advanced users program custom interfaces and controls that have access to every piece of information Ableton Live knows about the audio. The possibilities of extending the features of the application are limited only by the programming skill and creative needs of the user. I have used the software a little bit in school but I have not had the opportunity to program many of my own patches for any specialized function yet.
The following tutorial video shows how quick and simple some of these patches can be. Check it out: