ARSC Really Simple Chat
   A webchat software written in PHP and MySQL. It is compatible with every browser known today, even text-based ones. [Open source, GPL]
   http://old.manuel.kiessling.net/projects/software/arsc/

BlaB! Lite
   (formerly SimpleChat!) Fast, reliable, XHTML compatible web chat written in PHP and JavaScript.
   http://hot-things.net/blab_lite.php

Chatty
   A nice script that lets create a simple chat in a few minutes. Requires MySQL. [Open source, GPL]
   http://www.olivo.net/software/chatty/

Open Chat
   Features include unlimited and private channels; moderators, whisper mode, timed sessions and multiple language support.
   http://phpopenchat.org/

WebChat
   A chat application that features multiple rooms, no browser refresh, database back-end, emotions, private messages, and multiple language support.
   http://www.webdev.ro/products/webchat/index.php

Webfroot Shoutbox
   Allows users to post little blurbs on your website like a small guestbook/chat box. Inline or IFRAME, powered by mySQL.
   http://sourceforge.net/projects/shoutbox/

Wollabot
   Modular service bot for IRC channels.
   http://sourceforge.net/projects/wollabot/

X7 Chat
   A PHP chat script with unlimited users, rooms, and messages, IRC style commands, full message formating. [Freeware]
   http://www.x7chat.com/