Jabber @ RWTH - Present
The current system behind jabber.rwth-aachen.de is based on Debian/GNU Linux "Stretch" as the operating system, ejabberd from the official Debian Stretch Backports as the XMPP server and the Django based homepage from jabber.at, modified and extended for the RWTH Aachen University.
It has replaced the previous system consisting of Openfire, WordPress and handwritten PHP code. All relevant data was migrated during the process. The developed migrations scripts are published at github.com.
The system is hosted by the IT Center at RWTH Aachen University.
We use Ansible for deployment, the Playbook we wrote for that is published at github.com as well.
Both Django and Ansible are written in Python, ejabberd is written in Erlang. The migrations scripts are also written in Python.
Ansible Playbooks just like ejabberd's configuration files are written in YAML-Syntax. The tool 'yamllint' from Adrien Vergé comes in quite handy there.
Fancy statistics for the current system can be found here (only accessible from within the RWTH network).