Openfire is a real time collaboration (RTC) server licensed under the Open Source Apache License. It uses the only widely adopted open protocol for instant messaging, XMPP (also called Jabber). Openfire is incredibly easy to setup and administer, but offers rock-solid security and performance.
Most distribution bring openfire packaged and somewhat up-to-date, but to be on the safe side you should install the .deb or .rpm files from the developers homepage. Installation is pretty straightforward as configuration is done via the web-interface. You only need an up and running mysql (or mariadb) server and off you go. I will not go into installing said packages in this article, I assume you are able to get things running for yourself. If not, the remainder of this article is not for you – yet.
Issues start however getting a good grade over at xmpp.net: