Just wanted to mention I made lua-openmpt (https://github.com/konsumer/lua-openmpt/) which parses many formats of mod-files, if you have libopenmpt and luajit installed on your system. If you are already good with lua, you could use it to make a little script to extract instrument / song data. I have tested it in luajit & love2d, and it works pretty well.
I’m not quite sure how to approach a converter program. I have seen the technique of using specific samples, like from a template in openmpt, then converting that, but I wonder if we could go even further and convert samples into little wave-instruments, to get a base in there. For short things like drums & chiptune looping waves, this might work ok (but would probably need some serious post-conversion tuning.) I think a few other things might translate too, like jump or tremelo effect. If I could manage this method, I think it could also be used in the “load this template, edit it, and convert it” style, but also maybe handle some existing mods (even if they need a bit of tuning, after conversion) sort of like how I edit images in Gimp, then import them, and tune them in TIC-80 sprite-editor.
It seems like many of the links above are dead. Does anyone have some source I could look at of the existing work on this, so I have a good starting point? I’m on Linux, so an EXE isn’t really helpful anyway, but source would be great so I can see how it was done.