Olav Sorenson (aka 8bitbubsy) has made some very portable fasttracker 2 and protracker 2 clones using SDL and C. They seem pretty well built, though I’ve only used them minimally.
Sources on github: ft2-clone and pt2-clone. I can’t speak to the accuracy of the clones (EDIT: this ft2player project happened to be uploaded a few hours before I wrote this, so probably things are pretty accurate), but the code itself is pretty readable. I had a very pleasant time building and modifying the ft2-clone codebase to work on Alpine Linux (musl) using JACK (this was done before it was on GH): https://github.com/PaulBatchelor/ft2-clone.
I don’t know if it has been mentioned, but protrekkr is/was a surprisingly impressive 3rd-gen tracker.
It’s pretty fun, if you can manage you compile it. In addition to the usual sampler features you see in trackers, protrekkr had a built-in tb303 synthesizer, a subtractive wavetable synth, and reverb generator! I believe protrekkr is also related to noisetrekkr, which was the precursor to Renoise. You can kind of see it.
FalkTX added some JACK support on Linux (the repo above). For a while, I tried hacking on the codebase to try and integrate it with sporth. It was going to be a long-term project for me, but I gave up after a few tedious months. The codebase is a MESS, and was very rage-inducing. I concluded it wasn’t worth saving.