XMPP.is

Through our sister project, XMPP.is, Unredacted provides a free, open and secure way (with OMEMO or OTR) to chat with your friends on the XMPP/Jabber decentralized chat network.

XMPP.is has been around since 2015, and has arguably been one of the more well-maintained servers out there with a solid track record of stability. All of the scripts and configuration are open source as well.