Thank you Rob,
I was experimenting the Spreed.me feature under Nextcloud. It works very well however Nethserver needs to do some preconfiguration to the Tomcat server port 8080 is conflicting with many services.
I guess the same problem I faced with Spreed.me would be faced with Citadel.
Since my Tomcat is disabled now, I will try to install citadel and see if it works then write a how to if I was successful.