There's a new Jabber/XMPP server in town, running on Prosody (https://prosody.im
prolesphere.one | d7dchu2gnb4xce7y7vwmulonr4k2wh2dmobqyitwwjeiojfotrvw37yd.onion
Registrations are open, and so is room creation. The MUC (Multi-User Chat) server is at hive.prolesphere.one
The server supports OMEMO and OTR encryption, or should. Expect some growing pains in the early stages, there might be kinks to iron out so server may restart spontaneously. You can report any problems here in the thread or by messaging me at [email protected]
(not an email).
You can find a list of XMPP clients here: https://xmpp.org/software/clients/
I use Gajim on desktop and Conversations (available from F-Droid) on mobile.