ngIRCd
Free, portable and lightweight Internet Relay Chat server
...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 :-)