As Wikipedia says , XMPP is “an open, XML-inspired protocol for near-real-time, extensible instant messaging and presence information.” It’s used by Jabber, the Gizmo Project, Google Talk, Pidgin, Kopete, and all sorts of open source instant messaging applications.

It can also be used by any applications you want to develop yourself to pass messages back and forth, for example.

XMPP support in Ruby comes, primarily, from the XMPP4R library (Jabber4R and Net::XMPP are both semi-abandoned), and Frank...