X-Chat Common Lisp Plugin
The X-Chat Common Lisp plugin is a plugin for X-Chat version 2 and up (the famous UNIX IRC networking client) that allows you to use Common Lisp scripts to control X-Chat behaviour. You can basically do everything with a CL script that you could do with the C or Perl interface. It is also quite well documented. It uses ECL as Common Lisp implementation.

It is written and maintained by Julian Stecklina, is licensed under the BSD License and can be downloaded at its Sourceforge project page. You probably want to grab the 0.3 release. Happy hacking!