itch.io

OpenMPT is indeed open-source since 2004, and still in development, but the ModPlug Player for browsers (used on modarchive dot org (afaik) for online play of their database of modules) is closed-source. 

You can read about the history of how it was developed on the OpenMPT Wikipedia page.

I'm not a dev, but if this is written from scratch, I suspect support for these old formats would require an entire re-write of the codebase. OpenMPT also already supports all of those formats (to my knowledge), so the functionality would be a bit redundant, within this already niche scene. 

Just because the interface looks similar to other trackers, does not mean the software is handling all of the necessary legacy effect commands, or the audio itself, the same way. 

Beautiful art, as usual.

Very creepy stuff. The art and sound/music is on point.