Wollabot  

Wollabot is a modular service bot for IRC channels. It's written entirely in PHP making it crossplatform and easy to customize. It's not supposed to be guarding channels and does not contain such functionality thus increasing performance for the tasks it is supposed to do. It comes bundled with a couple of modules eg. a PHP function prototype lookup and a Google lookup tool.

Price: Free

   phpSmartIRCclass  

phpSmartIRCclass is a PHP class for communication with IRC networks, which conforms to the RFC 2812 (IRC). It's an API that handles all IRC protocol messages. This class is designed for creating IRC bots, chats and show irc related info on webpages.

Price: Free

   ZZ:FlashChat  

ZZ:FlashChat is a simple MySQL-based Chat Program with Flash-Interface. The advantage of using flash is that no annoying page refreshes are required for it to work. FlashChat is a combination of Flash, PHP and MySQL. For Installation you must have webspace with PHP and a MySQL Database. The client needs the Flash-Plugin (almost 98% have).

Hosting Requirements: PHP
Database: MySQL
Price: Free

   Simple Chat  

Simple Chat! is one nice and fast, HTML based chat-room written in PHP. The output produced by SimpleChat! is small and 100% HTML 4.01 compliant. Other features: Extremely fast loading (3-7kB/refresh); best viewed with any browser; no MySQL database required; easy text formatting; different icons, smilies, links; 20 color schemes at choice; protection against being framed; translated in different languages.

Price: Free

   Chatness  

A fast, simple, good looking chat script. Features include: easy to customize, shows users online, doesn't use any javascript, doesn't show ugly frames but cute iframes, and much more.

Price: Free

   PHP Chatengine  

PHP Chatengine is a complete chatengine designed to run under PHP, using MySQL as its database engine. The chat will only run on Internet Explorer (supposedly 4 and higher, but 5 and higher is more likely to proper without flaws), since it was designed to make use of some advanced D-HTML stuff. The sources to the various scripts that make up this engine, can be downloaded from this site. See below for more information. So forget about running standard Java Applets filled with commercial bullshit; it's time to run your own custom chat.

Hosting Requirements: PHP
Database: MySQL
Price: Free

   phpChatNvid  

phpChatNVid - based on phpOpenChat, uses the free webcamXp software for video broadcasting. Features: mail, open or closed site, private channels, ignoring, moderation, text filter, smiley interface and more.

Hosting Requirements: Linux
Price: Free

   Microcyb - Chat  

Microcyb Chat offers a new and easy way to chat on your site. This PHP chat script is a one file chat script, that offers image replacement, css style sheet templates, custom users skin selections, auto cleaning of old chat text, who is online, auto scrolling, and more.

Hosting Requirements: Unix/Linux, Windows
Price: $10

   paBox  

paBox is a PHP/mySQL shoutbox script (Also known as a tagboard.) You can add it to your site and visitors can post new messages, it is similar to a guestbook. Features: MySQL Backend, IP Banning, Flood Control, Smilies (clickable); Swearfilter; Multi Lingual Support; Admin CP; ADCP -> Edit posts; ADCP -> Delete posts.

Hosting Requirements: Unix/Linux, Windows; PHP 4.1.0+
Database: MySQL
Price: Free

   MWChat Pro  

MWChat is a robust, secure, and full featured web based chat system. MWChat was designed to be a real time chat that any user can easily add to their website and customize to fit their look and feel. MWChat provides buddy lists, file sharing, private messaging, user profiles, private rooms, and more!

Hosting Requirements: PHP 4.2.1
Price: $29.99