The Livegrabber plugins are a set of free Max For Live plugins that send actions from Ableton Live to any device on the network that supports Open Sound Control (OSC).
As of version 3, Livegrabber also allows the reverse: controlling Ableton Live with OSC.
Download the LiveGrabber 4.1 plugins here.
View the manual for more info on how to use the plugins.
For Max 5, use this version, but only on Mac OS.