Stoat (formerly known as Revolt) is a selfhostable, FOSS replacement for discord [Group chats and voice channels you can join any time].
Cool new name, however not as easy to use in other languages.
Voice chat is stil not officialy implemented.
Self-hosting there. Apparently nothing to do for you if you had already hosted before the name change.
The Android app has unfortunately disappeared (not been updated) on F-droid.
Edit: added short description for clarification
i honestly think that if revolt had federation, then it would be the obvious choice for me, but alas. personally i’m still hopeful for polyproto getting off the ground, but the boring realistic choice for the time being is probably something like XMPP + mumble