TLDR: The r/selfhosted subreddit has a Discord server. The owner’s account got hacked leaving the server in a precarious state. They submitted a support ticket, but Discord has not taken action in weeks and probably won’t at all, so they are considering starting a new Discord server.
Stoat chat has been a good Discord alternative.
What advantage does it have compared to Matrix?/IRC?
It mimics discord, so functional voice rooms with screen sharing, text channels, and so on…
Matrix has all that these days too
Fluxer as well. It has iOS and Android apps in beta too.