These are not necessarily the best, they are just the clients developed and released by the folks who run the actual IM systems.
AOL Instant Messenger
Authorized Third-Party Clients
Apple iChat (AIM)
Unofficial Multi-Protocol Clients
These clients are written by third parties, and are generally compatible with one or more of the above protocols. I have tried to weed out any clients that are no longer actively developed. The clients below have active developer communities and therefore are likely to be fixed if you find a problem with them. Also, if there is a protocol one of these clients does not currently support, there is a very good chance it will soon be added.
Proteus (AIM, ICQ, IRC, MSN, Yahoo!)
Adium (AIM, ICQ, MSN, Gadu-Gadu)
Fire (AIM, ICQ, IRC, MSN, Yahoo!, Jabber)
These clients run through X11, Java, or some other application layer on top of the Mac OS. Performance is probably not as good as the above native programs.
Jabber is a third-party IM system. Jabber servers are independently run, and the server itself does provide connectivity to other IM protocols. Since the application itself does not natively contain support for multiple protocols, it is listed separately. These clients will allow you to connect to a Jabber server at a bare minimum, and will allow interconnection to other IM services if the Jabber server supports it.
Note: This FAQ entry is by no means exhaustive. If you find something you think should be added to the list, please use the feedback/corrections link at the bottom of the entry.
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