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.
libircclient is a small but powerful library that implements the client-server IRC protocol. It is designed to be small, fast, portable, and compatible with RFC standards and most IRC clients. It includes multi-threading support, sync and async interfaces, CTCP and DCC support, and color support. Good documentation and examples are available.
ircproxy is an Internet Relay Chat Proxy, which works as a layer between your IRC client and the IRC server. It features bouncer capability and has more features, flexibility, and configuration options than other tools. It also includes an option to use the system password list instead of requiring a separate password database.
Darkbot is a very fast and small IRC bot written in C. Originally created as an aid for help channels to answer repeated questions from its virtually unlimited database, it has became a very popular talking robot in a generic sense, being used all over IRC networks for different purposes and in 18 languages. Data can be added to it and managed dynamically online or edited in its database files offline. An extensive but easy-to-understand list of commands and features, including some channel operation functions and levels of protection, makes Darkbot a very flexible but somehow powerful and complex robot, with almost human conversations and reactions.
TR-IRCD is an ircd and a collection of services programs for IRC networks. The ircd is heavily influenced by ircd-hybrid and Bahamut. It includes support for IRC extensions such as md5-encrypted hostnames, modules, threads, different protocols, channel modes, and languages. It supports IPv6 and Web-based configuration, and includes a proxy scanner.