Here is a(n unfinished) recipe for a modern chat server using XMPP (which you may recall I like). It needs polishing but I’m publishing it right now to make sure it can start being useful to anyone who needs it. I hope there are no glaring security mistakes, please let me know if you see any.
What do we get?
We will be able to get our messages on all connected devices at the same time, share pictures, audio clips and files simply and instantly, retrieve more chat history from the server and, once we go down in the metro and lose connectivity, get our messages when we regain access to the Internet.