EPIC4 is a new direction in ircII development. It was originally built upon the ircII-2.6 client and has maintained faithfulness to remain current up to the 2.8.2 release. EPIC is somewhat larger than the stock client (24%), but that is mostly because of the multitude of new features, the dual ANSI/K&R compliant function headers, and the large amount of re-written code in an attempt to make ircii faster, more efficient, and more powerful.
BSFlite is a minimalistic, line-based AIM client for Unix (including Mac OS X) and Win32. It is designed with simplicity and efficiency in mind and thus utilises as little RAM and CPU time as possible in order to be friendly to multiuser systems. It uses the OSCAR protocol to communicate with the AIM service.
PyGCS is a very stripped down MUD-like chat-server written entirely in Python. It has a single "room" and no large database to keep in memory and on disk. PyGCS has no embedded programming language. PyGCS is ideally meant to be a small multi-user real-time chat system for people who have a need to talk to more than one person at a time online. It fits somewhere in between the setup IRC uses (no walking between rooms so to speak) and the MUCK/MUSH/MOO style of server.
Damascus is a GTK+ 2.x client for the Gale communication protocol. It is somewhat modelled after IM/ICQ-style interfaces. If you don't know what Gale is, this client probably won't be very useful; you need a valid Gale key to send anything, and Damascus can't generate them (yet). Gale is also scary and confusing.
BitchX is the premiere IRC (Internet Relay Chat) client. It originally was a modified version of the popular ircII client, and the features were eventually merged into the EPIC IRC client. The current development is aimed at merging the client back to a current branch of EPIC and bringing compatibility and stability back to the client, while bringing the features that are BitchX into a new client.