See also http://ftp.math.utah.edu/pub/hoc/ - Maybe I should have pointed to this for hoc7 vs. the manual?
There’s not a clear LICENSE file. The string GPL appears at the top of one or two C files, but it’s not clear to me if these are libraries, or part of hoc. It’s possible that the information I seek is present but I just don’t know what I’m looking at. (As a merely level-one software license nerd, I pretty much need a LICENSE file…)
I know that OpenBSD includes hoc6 aka AT&T hoc in the ports tree but not hoc7 - I have not investigated the reason either, but it might be licensing related.