Science, Technology, and pawbs
There's Matrix, which is federated (diff protocol than ActivityPub, though). It seems decentlly active but atm maybe one of those things where you need to already know people who use it to be able to find the good stuff, because I'm struggling to find much of anything I like (but I've also been dodging the larger groups because I'm nervous lmao)
There's also XMPP or Jabber as it used to be called, which is better for 1-on-1 type conversations, but group chats are also a thing there.
I see, but I don't think I know anyone who uses it. I know matrix has a public channel, but is the public channel decent? I'm honestly kinda nervous to jump into a new platform-- I'm already nervous enough to post anything on a platform I'm already familiar with
Matrix is quite popular in Europe. German police and army uses it in their private instances...
There are a ton of programming channels that are very active: Rust and NixOS are the ones I follow.
I think the best implementation so far is Beeper, where you have all the bridges to different chats together with Matrix. I run it so I use the same app for Signal, Telegram, Whatsapp and LinkedIn. You can set it up by yourself too, but Beeper makes it very easy. They open to public later this month.
I don't use the big generalistic Matrix channel so I can't say, but I'm in a smattering of groups for programming topics I'm interested in like Godot and they're really nice.
If it's just text, you could always go back to IRC https://en.wikipedia.org/wiki/Internet_Relay_Chat
I believe Matrix has all the same text and call features as discord, but I haven't tried it. Apparently there's also bridges you can run to mirror a discord into your Matrix instance.
#cyberfurz-official:cyberfurz.chat and #home:furs.chat are good spaces to join if you go with Matrix, maybe others could also chime in if they know any!
How many people are in those spaces, and is it active? I'm currently looking for a laid back trans/lgbt matrix chat, but it's been somewhat hard to find. And there are a few very obscure stuff I jouned on discord that won't be on Matrix.
I might consider the idea though
25 and 42 respectively, it's not super active, but not dead either, if you're on masto you probably recognise at least a couple people there already.
I'm on Mastodon, but I mostly follow #lgbt related stuff, that's what I've been looking for
While it might not be fediverse based, I've been keeping an eye on an alternative cough clone cough called Revolt since they're aiming to have it be self-hostable.