"Jabber, the streaming XML technology mainly used for instant messaging, is well-suited to its most common task. However, Jabber is a far more generic tool. It's not a chat server per se, but rather a complete XML routing framework. This has some pretty far-reaching implications.
"Technically speaking, Jabber can act as a router for anything that can be represented in or with XML. Since it's mostly used for online messaging, and since clients for Linux are readily available (GAIM, for example, is a Jabber client, there are many, many more), I'll focus here on ways to use Jabber to send informational system messages to a Jabber client (or clients)..."