FaceTime? It probably doesn't work at conference scale but it is E2E.
> We designed iMessage and FaceTime to use end-to-end encryption, so there’s no way for Apple to decrypt the content of your conversations when they are in transit between devices.
As a user of macOS, I want developers who makes apps to use public APIs that will be supported so I don't get breakages on system upgrades or migrations.
https://apolloapp.io/