Reminder:

Every Nerdculture user can use XMPP chat with the same credentials - now even with audio/video calls when the client supports this feature, e.g. Conversations on Android.
You can find more information here: https://hookipa.net/nerdculture-xmpp-server/

So get a XMPP client and start communication via XMPP! You can find more information on https://hookipa.net