I've been making accounts with and trying a ton of different solutions. Would love to hear what other folks have found or if you've found things that have drawn you to any of these platforms that I've overlooked.
https://stoat.chat/
Stoat is the closest in vibes to what Discord is, but I'm frustrated with the inconsistent feature set across web/mobile/desktop and have found it frustrating to use. I don't enjoy it.
https://matrix.org/
Matrix seems to have a lot of good functionality but the way it's set up has been difficult to wrap my head around. Specifically creating a space appears to be less like creating a server and more like a folder for a group of different chat groups that may or may not be shared by other Matrix users? So instead of joining a Discord server with an announcements and rules channel, someone could piecemeal grab those channels and bundle them in their own group I think? I'm not sure, could be a me problem.
https://www.rootapp.com/
Root seems pretty robust and well made, but it's privately owned and does not allow NSFW content at all.
In addition to chat I've been looking into forums. I haven't tried these yet but they're options I've been made aware of.
https://github.com/discourse/discourse
Discourse
https://www.phpbb.com/
phpBB
https://freeflarum.com/
Freeflarum (this forum)
So far I'm pretty excited about Freeflarum. This was really easy to set up and if I understand correctly, it has the capacity to be migrated and self hosted. Still open to looking at other solutions but really happy with how easy this is to work with.