MIDI Monitor is a utility for Mac OS X which displays MIDI signals in a variety of formats. It can watch both incoming and outgoing MIDI streams, and can filter them by message type and channel.
Convert your guitars analog signal into MIDI.
It lets you hook up your various pieces of MIDI software and hardware.
Application that takes standard MIDI files.
Bome’s Midi Translator Pro is a popular MIDI and keystroke mapping tool.
Nifty application, providing MIDI-related tools.