IRC still supports most of the FOSS core.

More modern alternatives include Jitsi, Matrix and Simplex. Mumble also works well for voice.

You’re gonna need jitsi too. Simple is more secure but the client is heavier than matrix. You can run a server but shouldnt need to

It’s dead. The development has been as fraught as Tox and it has no feature parity. Not sure it’s worth forking.

Right now your best options are jitsi for video or good old mumble for voice and simplex or matrix for text chat.