Developer Geert Bevin (Eigenharp, LinnStrument, MPE) has released a free command-line utility for receiving and monitoring MIDI on OS X, ReceiveMIDI.
ReceiveMIDI complements a utility that he released in January, SendMIDI. Here’s what he has to say about ReceiveMIDI:
ReceiveMIDI makes it super easy on MacOS, Windows or Linux to monitor a particular MIDI device and to freely unplug and replug it.
There are a series of handy filter commands if you just want to focus on some of the messages, and you can optionally add timestamps. This goes hand-in-hand with an update to the SendMIDI tool that now understands these timestamps, allowing you to play back anything you saved and edited from ReceiveMIDI, with the appropriate timing.
ReceiveMIDI is free and open-source, and can be downloaded from Github.