(i haven't seen it mentioned in this sub. it has improved quite a bit since its inception. it deserves some credit🥂)

Jami is a free/libre, end-to-end encrypted and private communication platform that requires no central authority.

Multiple devices can be linked to a Jami account, and no personal information is required to create an account.

What features does Jami include?

• Instant messaging
• Audio and video calls
• Swarms (group chats)
• Video-conferences and Rendezvous points with no third-party hosting
• Audio and video message recording
• Screen sharing and media streaming
• Built-in extension platform for new features and experiences
• Jami can also function as a SIP client

Jami uses a distributed hash table (DHT) to connect peers. Jami accounts are asymmetric X.509 certificates generated by the GnuTLS library. Calls are made over the Session Initiation Protocol (SIP) after negotiating a TLS-encrypted secure connection, performing Secure Real-time Transport Protocol (SRTP) communication which carries the media streams.

https://jami.net/