An IRC client for use with Microsoft Windows. It was written by Mark Hanson, and the last version (1.0b4) was released in 1997. Active development is no longer done.
It is distributed under the terms of the BSD License, however, the source code has not been released to the public, or for continued development by other programmers.
XiRCON offers "instant usability" (i.e. you don't have to spend hours configuring it, before being able to use it) and "unlimited configurability" through its scripting capabilities. Scripts can be written in TCL, with the special editor that comes with the IRC client.
Personally, I like XiRCON, because it's fast, small, it looks neat, and I don't have to reconfigure everything when I move to another computer.