As the maintainer of InspIRCd i'm biased towards it but ngircd is a pretty solid piece of software if you only want something which is simple and easy to set up

As the maintainer of InspIRCd i'm biased towards it but ngircd is a pretty solid piece of software if you only want something which is simple and easy to set up without a bunch of fuss. I have to look through the source code of other IRC server implementations regularly when checking for cross-server compatibility and looking through ngircd's source code is always a pleasure. Its extremely well written and easy to follow unlike the irc2-based IRC server implementations (UnrealIRCd, etc) which usually are a pain to find out what they're even doing.