The Snoize MIDI Monitor is an open-source software utility for Mac OS X (version 10.3.9 or later) that displays MIDI signals in a variety of formats. Particularly useful for testing and implementing MIDI equipment in live show environments, it can watch both incoming and outgoing MIDI streams and can filter them by message type and channel.
Lately I’ve been experimenting with various MIDI hardware interfaces for lighting control consoles and video control software that allow for more tactile ways of playing back both lighting and video cues. Very often it is difficult to confirm what the hardware device is actually outputting. This makes mapping MIDI information to the controller a very tedious process. MIDI Monitor takes all of the guesswork out of such tasks by displaying what your hardware device is outputting in real-time. Installation and setup are remarkably easy and, best of all, it's free.