MilkyTracker
I love MilkyTracker for its minimalist Amiga tracker-esque experience, but have been frustrated by its instability on macOS. You really do have to save your work very frequently in order to avoid losing it so I've found myself gravitating towards Renoise, even though it's paid and - very recently - Deflemask (I also like that it supports SID tracking, which is what I've been playing with).