In Max everything can be connected to everything, because everything speaks numbers. Another way to say this is that modularity is a core design principle of everything in the software.
Max can control MIDI devices, serial devices, send data over a network, and handle user input devices. Any source of control is easily connected to anything you want to control. Most commonly, however, Max’s powerful control features are applied to audio via MSP and visual media with Jitter. And MSP and Jitter offer their own control possibilities, from audio signal analyzers to video tracking and device support.