I think ejabberd or another other xmpp server would have been my first choice for a service like this by a long shot. If only we had some good iOS clients to go to. While I’m on android, most of the family and some of the friends use iOS, so it was kind of a non-starter from that alone.
Edit: log -> long
Telegram’s server side software is closed source, owned and ran by them exclusively so they really have no room to talk. WhatsApp doesn’t even have OSS clients so they’re even worse in that regard