ICQ, as in "I Seek You" is a proprietary piece of freeware that allows you to monitor when your friends are on line and enter into live chat with them.
Many people like it. I can't stand the constant interruptions. Each time someone see you on line and has a few minutes to talk you get this annoying "Uh-Oh" thru your speakers. Gr-r-r-r!
I believe it may be downloaded at http://www.icq.com.