Smuxi is an irssi-inspired, flexible, user-friendly, and cross-platform IRC client for sophisticated users. Smuxi is based on the client-server model: The core application (engine) can be placed onto a server which is connected to the Internet around-the-clock; one or more frontends then connect to the core. This allows the connection to IRC to be kept up even when all frontends have been closed. The combination of screen and irssi served as the example for this architecture. Smuxi also supports the regular single application mode. This behaves like a typical IRC client; it doesn't need separate core management and utilizes a local engine that is used by the local frontend client.
The Tcl IRCd is a small IRC server written in Tcl. It is very simple to modify. It is not a full implementation of the IRC protocol, but it's enough to create channels, talk in public or private, change topic, nick, and other basic operations. No configuration is required. The server is designed so that it can reload an updated version of itself at runtime without closing client connections.
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.
dxirc is a easy-to-use yet capable cross-platform IRC client. Among its notable features are flexible configuration, a fully customizable look independent of system-wide settings, multiple server support with optional automated joining of selected channels, and the ability to connect via SSL.
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.