When registering on Outmo.de you automatically get an XMPP (aka Jabber) account on the same user ID.
So if your Fediverse ID is
firstname.lastname@example.org you can also be reached via the XMPP federation on the same JID.
Learn more about XMPP on Joinjabber.org.
You can use the F-hub.org XMPP invite page to share your contact and invite other XMPP users to chat rooms.
We currently recommend the following mobile apps for XMPP:
There is still some work to do to enable video calls on our Ejabberd XMPP server. Hopefully we will be able to enable it by the time Monal has full support for it as well.
We will also support using XMPP as a UnifiedPush distributor.
We will also try to integrate a XMPP web-client into our Akkoma frontend.
There is also a plan to enable some Slidge gateways to other chat services like Telegram or Signal.