IRC clients

IRC is the grand-daddy of all instant messaging, and so there is a vast 
range of clients for all platforms.

If you google IRC client, your will see some of the choices. See 
(http://www.ircreviews.org/clients/) for a list of the better known 
clients.

Personally, since I don't use Windows, I have no opinion on Windows 
clients.

For unix and for Mac OSX a good (if somewhat complicated to use) client 
is xchat and xchat-aqua respectively. xirc is also a good client for 
macs.

Although there are many IRC clients, most fall down at the first 
corporate firewall. However, xchat knows about proxies and firewalls 
and can route round them -- using normal HTTP proxy settings.

Frank