Miranda IM
This program is an alternative to all Chat programs, Instant messengers and whatever it is called. The program has support for various protocols(ICQ, MSN, Jabber, Yahoo, IRC and more).
It is highly customizable. You can change the look and feel to how you like it. There are thousands of plugins for this little program.
E. g. you can have RSS/ATOM feeds downloaded and get a popup message. Or you can have a weather forecast. Almost anything is possible to configure.
Here is a little picture of how mine looks at the moment. I use it for IRC channels, MSN, and feeds (As GMail user I can receive news from my inbox through an ATOM feed). I have found a premade skin on the Internet.
Finally, a link to the Miranda IM Project.