just music controllers, unless you are converting the data from whatever it is you’re getting the information from into MIDI, then using that MIDI information to control say an analog synth, or a VST, or some patch.
There is an important distinction to be made between control rate (messages such as MIDI or other generic controller input) and audio rate (signals). See "How MSP Works" in the Max documentation for more info.
"MIDI" stands for Musical Instrument Digital Interface, and is a protocol used to send numerical data that was first standardized in 1982, and is used in most synthesizers, electronic keyboards, etc. along with many cell phones and computers. MIDI can also be used in the way you described- to control parameters of a computer program using the data from a Wii Remote or a patch that tracks color. Not all controllers are MIDI controllers though, it is just a particular method for sending data that works when working with "instruments". Check out OpenSound Control and other methods of sending data for more info and alternatives!