infobot is an IRC bot written in Perl 5 which implements a sort of artificial intelligence by learning information ("factoids") from channel discussions and then responding intelligently to queries about this accumulated information.
In the beginning, we had to type URL's out, or, at best, wade through a set of hierarchic bookmarks for a URL. But what about when you don't know what you're looking for? If you just want to name it, and find out where it is? (Of course, archie has done this for years.)
What makes infobots different from a lycos or a set of bookmarks is that he learns by observing, and that you can query him in intuitive ways.
Internet Relay Chat is a set of client and server which use a protocol. People get on and chat in near-real-time; rather than wait for your netnews replies, you can ask a question and get ignored or answered while you wait.
Url has been sitting on the EFNet channel #macintosh, where he's picked up quite a few factoids from the local community*.
Url, purl, and rurl are perl scripts that once ran under sirc. In fact, it would also run under MacPerl and my barebones port of MacSirc. However, I ended up writing a little irc front-end for it of my own because sirc would hang (rather than, say, crash gracefully).