WeeChat is a fast, light and extensible chat client. It runs on many platforms like Linux, Unix, BSD, GNU Hurd, Mac OS X and Windows (cygwin).
Pro Intuitive, detail-oriented interface
By default WeeChat has a chat area surrounded by a nicklist on the right, title bar on top, and status and input bars at the bottom. The layout, though, can be completely customized and split vertically or horizontally. It supports 256 colors as long as the terminal supports 256 colors as well as bolded, italicized and underlined text. Even includes little touches as differently colored nicknames for people /away.