It's more of an alternative/competitor than "Hacker News for x", but https://lobste.rs/ seems active.
Datatau seems to be alive, and I check it regularly. Not much discussion though. http://www.datatau.com/
Regarding DataTau I built a small front page analyzer and have some graphs up. It runs every 3 hours and looks at some aspects of both HackerNews and DataTau and compares the two. It's still very much a work in progress. At one point I will let it run for an extended period of time.