Wraith is an open source IRC bot written in C++. It has been in development since late 2003. It is based on Eggdrop 1.6.12 but has since evolved into something much different at its core.
BitchX is an IRC client based on ircII/EPIC4. It includes many features that are usually relegated to scripts such as CDCC and flood protection -- you can just start it and go. Development was on hiatus for a while but is now resuming.
dxirc is simple IRC client
jIRCd is a full-featured Java-powered IRC server. It uses the advanced features of Java, including multi-threading and multiple platforms, to create a very powerful IRC server for any platform.
libircclient is a small but powerful library, which implements client-server IRC protocol. It has all features needed to create your own IRC client or bot, including multi-threading support, sync and async interfaces, CTCP/DCC support, colors, SSL connections and so on.
Free, portable and lightweight Internet Relay Chat server
ngIRCd is a free, portable and lightweight Internet Relay Chat server for small or private networks, developed under the GNU General Public License (GPL). It is easy to configure, can cope with dynamic IP addresses, and supports IPv6, SSL-protected connections as well as PAM for authentication. It is written from scratch and not based on the original IRCd. The name ngIRCd means next generation IRC daemon, which is a little bit exaggerated: lightweight Internet Relay Chat server most probably would have been a better name :-)
Ident server with masquerading support
Oidentd is an ident daemon (rfc1413) that runs on Linux, FreeBSD, OpenBSD and Solaris 2.x. Oidentd supports most features of pidentd plus more. Most notably, oidentd allows users to specify the identd response that the server will output when a successful lookup is completed. Oidentd supports IP masqueraded connections on Linux, and is able to forward requests to hosts that masq through the host on which oidentd runs. This is a fork of the ojnk oidentd released in 2006
srvx IRC Services is a ground-up implementation of services for IRC networks (supporting IRCu2.10, Bahamut, and other IRC server dialects). Features include POSIX threading, generalized proxy detection and all the standard services users expect.