I remember the PowWow McAfee founded that did collaborative web browsing.… http://en.wikipedia.org/wiki/PowWow_(chat_program)
I think this was also one of the first applications that could qualify as an instant messaging tool. I remember it coming out well before ICQ and AIM. I hope the guys working on this project don't end up mired in trademark issues.
I would certainly consider IRC to be an instant messagig tool, and that has been around since around 1988, while the orginal PowWow seems to be from 1994, which would make it 6 years late to be first. The most well known networks like ICQ and MSN came some years later, so they were still early.