XMPP allows video conferencing. Jitsi https://jitsi.org/ is probably the most mature and usable XMPP client in that front and has clients on every platform. (even in the browser with Jitsi Meet)
Ring works really well, I'd recommend it if you have an SIP server, but the server-less part only relies on OpenDHT to connect another user, which is troublesome. https://ring.cx/en/about/privacy-and-anonymity
Tox https://tox.chat is really promising, but many clients are buggy, some even leak, and the security is not reviewed.
RetroShare has a VoIP plugin, but the client requires a little bit of learning curve and mobile support is very limited.