My first thought was "great, all those are proprietary* and centralized. maybe they'll use XMPP or Matrix", but I see people mentioning Threema. I'm not familia

My first thought was "great, all those are proprietary* and centralized. maybe they'll use XMPP or Matrix", but I see people mentioning Threema. I'm not familiar with it. A glance at Wikipedia shows the protocol is MIT and the apps are AGPL, so that sounds good anyway. Signal may not exactly be proprietary, but they won't put it on F-Droid, so... Telegram has a free-ish client but not a server