Created at MIT, as part of Project Athena, Zephyr was designed as an instant messaging protocol and application-suite with a heavy Unix background. Using the "do one thing, do it well" philosophy of Unix, it was made up of several separate programs working together to make a complete messaging system. Zephyr and IRC are the first widely used IP-based instant-messaging systems.
Zephyr is the invention of Ciarán Anthony DellaFera who was, at that time, an employee of Digital Equipment Corporation and a Visiting Research Scientist at Project Athena. The design originated as a solution to the "reverse Remote Procedure Call (RPC)" problem: how can service providers (servers in a client–server system) locate and communicate with service users. The initial concept emerged from conversations between Ciarán and Michael R. Gretzinger, another systems engineer at Project Athena, in early 1986. By mid to late 1986 Ciarán had distilled the problem to two specific issues: the ability to locate users in a distributed computing environment (known today as "presence detection"), and the ability to deliver scalable, light-weight, and authentic messages in a distributed computing environment. The Zephyr Development Team (Mark W. Eichin, Robert S. French, David C. Jedlinsky, John T. Kohl, William E. Sommerfeld) was responsible for the creation of the initial code-base and the subsequent releases that were issued throughout the late 1980s.
Zephyr is still in use today at a few university environments such as Carnegie Mellon, Iowa State, University of Maryland, College Park, Brown University and MIT. It has been largely replaced by modern and more popular instant messenger systems such as XMPP. MIT currently operates both Zephyr and XMPP.
Points of interest 
Zephyr uses UDP datagrams sent between ports 2102, 2103, and 2104. It is incompatible with most routers doing NAT because it reports the internal IP address and so returning datagrams are incorrectly routed. Most sites have deployed Zephyr using Kerberos 4 authentication exclusively, though in late 2007, some sites, including Iowa State, deployed Zephyr using Kerberos 5.
Client Support 
- Multi-protocol IM client BarnOwl has always had Zephyr protocol support.
- Multi-protocol IM client Pidgin supports the Zephyr protocol since version 0.11.0-pre10 (April 13, 2001).
- Multi-protocol IM client Adium added support for Zephyr in Version 0.70 (October 18, 2004) and dropped support in version 1.4b6 (June 3, 2009).
See also 
- Zephyr 3.0
- The 1988 Usenix paper on Zephyr
- Zephyr on Athena
- MIT Q&A about Zephyr
- Zephyr's Source Code