Zephyr (protocol)
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.
Read more about Zephyr (protocol): Creation, Application, Points of Interest, Client Support