The current distribution Arc Lisp can be found at https://arclanguage.org. It ships with a forum that isn't up to date nor does it have feature parity with HN, which is kind of its own black box because Real Money is involved, and Real Money ruins everything.

Also there is a public fork of Arc Lisp at https://arclanguage.org/anarki, which is not guaranteed to be stable, and ships with a forum which is definitely not to feature parity with HN.