Quassel IRC is a modern, cross-platform, distributed IRC client, meaning that one or more clients can attach to and detach from a central core, much like the popular combination of screen and a text-based IRC client, but graphical. In addition to this unique feature, it aims to be a comfortable chatting program.
123 Flash Chat Server is a full-featured chat server for high-load Web sites. It features a range of customization options, and can be smoothly integrated with the database of almost all leading CMS or forum systems including Joomla!, phpBB, skadate, and vBulletin. It includes plain text chat and video chat options, and is scalable enough to fit the needs of small business and large enterprises. A free 10-user edition is available. It's based on a Java server and a Flash client, but also has various alternative clients based on technologies such as HTML/AJAX, so it can run on many platforms, including iPhone and iPad. It features avatars, smilies, Flash emotions, voice messages, entering multiple rooms, dynamic skins, loading external avatars and profiles, and a media player. The HTML 5 client significantly improves the chat performance in terms of loading speed, video layout, and user interface.
The SeaMonkey project is a community effort to develop an all-in-one Internet application suite. It contains an Internet browser, email and newsgroup client with an included Web feed reader, HTML editor, IRC chat, and Web development tools, and is sure to appeal to advanced users, Web developers, and corporate users. It uses much of the Mozilla source code powering such successful siblings as Firefox, Thunderbird, Camino, Sunbird, and Miro.
php Free Chat is a simple, fast, and customizable chat server that uses the filesystem for message and nickname storage. It uses AJAX to smoothly refresh and display the chat zone and the nickname zone. It supports customized CSS stylesheets and a plugin system that allows you to write your own storage routines.