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