Instant messaging is great for one-on-one chats, but it’s not optimized for group chats of 3 or more people. Further, instant messaging is network dependent — if you are on AIM, and your client is on MSN, you can’t instant message.
Campfire, on the other hand, is all about simple and quick network-agnostic group chats. It’s a self-contained, password-protected web-based chatroom that allows groups of up to 30 people to chat and easily share files together. No instant messaging software is required — all that’s required is a web browser.