Oh wow, Zoltan was one of my lecturers at UniMelb, and in one semester we were tasked with learning his Mercury language. So good to see it thriving still.
The closest that I could find to a "what the fuck is this?" page is:
There are files in this repository that were last touched 32 years ago. Any reason to be posting it now?
Last release was in 2023.
It is effectively dead.
This is a terrible shame, because this would have been an nice modern alternative to Prolog.