LimeChat is a Mac OS X IRC client available for Snow Leopard, Lion and Mountain Lion. LimeChat offers several functions that are different from other common OS X IRC clients, such as the multiple server/channel window. This window is shown at the bottom of the screen and shows all activity from the servers and channels you are connected to - and if undesired, all you need to do is drag the typing bar down and hide this window, leaving only a window for the channel you have selected. Being a long time user of IRC, this feature seems very useful to me, although it would take some time before I got used to it.
Another feature of LimeChat is the ease of using the keyboard shortcuts - all OS X IRC clients I've tried have keyboard shortcuts, but some use more obscure keys for their shortcuts. I was pleased to find that LimeChat offers easy to use and remember shortcuts (a main list is found on their website).
Despite these useful features, I do have a couple of complaints. A major problem I ran into was the lack of different nickname colors, something that is extremely important to me for ease of reading an active channel. My other complaint has to do with the interface design. The default theme, while not terrible, doesn't feel polished to me and the yellow and white text are, for lack of a better word, unattractive (although this is of course merely a matter of opinion). If this theme was able to be customized more, I think I would quite like it. There is an option to change themes, but the others I found to be not much better.
Beyond these two issues, I think LimeChat is a great IRC client - and being free, I hardly feel I should complain much about the problems I ran into. It offers a wide range of functions and I think that once used to the layout and design, any IRC user could make great use out of it. And if interface design doesn't bother you, I'd say this is an excellent client to try.
