Except that the AIM protocol was reverse-enginnereed and you could then use a single client (GAIM/Pidgeon, Trillian) to talk to all your friends. The protocols nowadays are so locked down that there has yet to be a decent 3rd party implementation.

The AOL chat rooms were different than AIM.

From the chat room you could open instant messages to specific people, and that one-on-one chat eventually became AIM.

For one-on-one messaging, the 3rd party clients were often better, but I don't remember any 3rd party clients for the chat rooms. I only used them from the AOL application itself.

Loved Trillian