I used to use my osx box at work to compose on, but I can't remember the name of the tracker I worked with. It reminded me of Alice in Wonderland's Cheshire Cat for some reason. : (
I ran some google searches, and Milky Tracker looks kind of cool:
http://www.milkytracker.net/?HOME (free)
I mostly use ModPlug Tracker (or Open ModPlug Tracker), but I've only seen builds for Wintendo, unfortunately : (.
Once I'm off of my vacation, I can check the computer there and link you to it).