Jabber  BBN Presenter.  Book.

Brief background (streaming protocol, XML based)

Clients implement subsets of protocol.  Server maintains little user state.  Keeps track via <userid>.xml - presence state, roster, etc.

Because it retains little state, easily transfers state from endpoint to endpoint.

jabberd extension via direct lib modules (dll / .so)  Components can tie on remotely (over net etc).  Configuration via jabberd.xml (apache model)

Example of stream message to open connection.

Discussion of libraries 
    Jabberbeans
    J-XMO
    b9j2 (new java lib)
    python libs
    ruby libs
    perl libs
    
XMPP elements
    <presence>
    <message>
    <iq> - info query (primarily server interrogation)
    
XML namespaces qualify elements, and Jabber IDentifies look similar to email with the addion of a resource (used for example, for routing.

(eample message).  Incorporates a threading identifier (bas64 in example - may be worth investigating).  Compare to well formed jabber msg spec

Sample java codelet.

Example of service browsing (interrogation for services of a particular host)

Presence example - from includes a resource.  Can be generated on behalf of a particular user/resouce (how is this guaranteed?)  Note also that this includes both state and status (state and message)

BBN using for distributed testing - DARPA UltraLog project.

Example project 0 a distributed jpg filetransfer server. 

Summary:  Monetising, IM not just for chat, Jabber robust and open.