When it comes to @Delta Chat (39c3) do you know it features 1 to 1 audio / video calls since v2.22?
It has a very lightweight client side app built with web technologies and a minimalist server side component turn server called chatmail-turn.

I am wondering, am I alone running that turnserver behind a nat?

github.com/chatmail/chatmail-t…

Added commandline arguments and functionality usefull to run behind a NAT by pvagner · Pull Request #7 · chatmail/chatmail-turn

This turn server enumerates all the interfaces found on the system, identifies globally addressable addresses and creates an UDP listen socket on the default port. Relay connections for this scenar...

^GitHub