Matrix is the federated alternative.

These are all looking like they are becoming good replacements. However, they will have to beat the challenge of adapting to the sudden high influx of users when none of them are fully ready:

Fluxer.app (Open Beta)

GaneVox (Open Beta)

Spacebar.chat (Open Beta)

Stoat (Open Beta)

Language model integration, at the core. But only if you want it.

Nah, not installing anything that uses this shit, even "optionally".

https://joinmatrix.org/ feel free to use any of the servers If you want a UI similar to discord, you can use https://commet.chat/

Some people in my communities are looking at Root, it lets you directly import a discord server template when creating a server. It has a nicer UI than all the matrix apps and stoat, but isn't as open as those.

Matrix, Fluxer, Zulip are what I've heard.

I'm assuming that you aren't wanting Threadiverse-based stuff like !retrogaming@lemmy.world?