Textual is an IRC client for the Mac that I recently started using in favor of xChat. Right off the top I’m going to say that it’s super customizable. I’d say that’s the number one feature — especially if you do the whole CSS thing. I’m surprised there aren’t more themes available, but I guess it’s probably pretty new.
It’s also a very functional application, but doesn’t get in your way. I’d also note that the development team was quick on the twitter response to a feature request, but we’ll have to see if those requests actually ever make it into the app.
It can’t hurt to checkout this lightweight app if you’re ever in IRC — irc.smmas.com #smmas every Thursday night for the smmas live chat, or smmas.com/live for more info. I’ll also include a link to the css for my custom version of the Dark theme.
Update: Now with inline Nick highlighting supported: Download v1.1