4 pane comic of dolan on the left and spooderman on the right
pane 1 (dolan): cum join opensurce cummunity!
pane 2 (spooderman): shure! how joyn?
pane 3 (dolan): Here discord! (with discord logo)
pane 4 (spooderman with tears in eyes): y u do dis?
A web forum is far better in most cases. If you can't manage to run your own, there are plenty of lemmy servers that will do it for you. Even an email list (with searchable archives) would be better than Discord.
If you have collaborative documents that outgrow the forum format, use a wiki.
If real-time chat is needed, irc or matrix.
A project hosting its community on Discord is a project that won't get my contributions.
It's sad when a web forum is better than the tool you're considering. Bumps, aggressive garbage collection, no Resurrection, it's weird.
I'm old, I guess. I miss NNTP, mainly for the archived posts I could discuss with the authors for an updated take or revised solution or some clarification. And yes, I know there's a good webUI front-end for an NNTP server as a back-end. ;-)
On the bright side:
Aggressive garbage collection and automatic thread locking are optional settings in most web forum software I've seen.
Lemmy shares some of the important parts of Usenet, and could develop into something that comes close.