I just updated JEP-0174: Link-Local Messaging. This specification describes how to communicate in an XMPP-like fashion on local area networks, at WiFi hotspots, etc. -- all in a way that is interoperable with Apple's iChat. It's a cool feature since it enables you to chat with other people even if you don't have access to a public or private Jabber server, plus it's being added to more Jabber clients now that we have documentation for it. So go forth and implement! :-)