And if you want something realtime, IRC & XMPP are low-resource chat options—with the latter being federated & can offer encryption for private rooms.
Sure, but those options solve literally none of the issues discussed above
There’s still been a time & place for realtime communications where the history preservation doesn’t quite matter… it can be some general recon of a problem to know what to even ask so as to not clog up the signal-noise for SEO or even if it’s mostly off-topic banter to relate to community members.
I’m thinking of a rapid alert on a problem in the project using IRC/XMPP/Matrix and then the project managers posting it in a forum about problems in the project.