Ask HN: Technical chat (slack/IRC/discourse/etc.)

what are some good technical chat rooms for various topics? there are a couple rooms on irc that are active (e.g. #math and #physics) but otherwise i can't find anything.

ml, cs, ee, would be nice. there are a couple slacks associated with udacity courses (and such that) that have run but they're spammed to hell by now.

edit:

this collection looks decent

https://www.discordnetwork.com/