XMPP , an acronym for eXtensible Messaging and Presence Protocol, is the generalized XML streaming protocol that underlies Jabber.
XMPP was used by Google Wave.
RLH 2009-06-01: Does Tcl have anything library wise that talks xmpp?
tclxmpp. New projects should probably use this library.
There is also a server-side daemon called tclxmppd.
DKF: XMPP can also be used as a transport protocol for SOAP, which is helpful for when you have long-lived webservice communications between two parties (especially when one party doesn't want to open incoming ports in their firewall).