[ excerpt from developer's www site ]

Jabbr is an OCaml library for the XML Messaging and Presence Protocol,
more commonly known as Jabber, based on my Yaxpo reentrant XML
parser. Jabbr provides basic XML stream and authentication services
based on a clean state machine abstraction which imposes minimal
constraints on the underlying I/O mechanisms used by the driver
program. It currently does not provide automated support for
higher-level XMPP abstractions like presence and roster management.

In addition to Yaxpo, Jabbr requires Xavier Leroy's Cryptokit
library, which provides SHA-1 hash support for authentication.

WWW: http://mikelin.mit.edu/xmpp/jabbr/