Yes, can use Discourse for async, long-term communication. Or Flarum if you want something more modern feeling (but with a lot less features).

And then Matrix for real-time chat. Bridge it to IRC if you want. Search is not great in Matrix but sufficient for simple keyword searches.

I just checked out Flarum the other day, why is it more modern? I actually found Discourse is still much better. Flarum does not even have nested reply threads as far as I can tell, it's all flat and hard to read for any thread of replies.

I far prefer Discourse myself, and it is superior in useful features. "More modern" is mostly what I heard others saying in response to me recommending Discourse. Suppose it is a look&feel thing mostly, and personal preference. That said, you can customize Discourse quite extensibly.