Adium is probably one of the most used chat clients on the mac. It not only allows you to use all the networks iChat does , but it also has support for many other networks as well. The list includes Live Messenger, Yahoo, ICQ, Facebook, Lotus Sametime and many others. Oh, and it’s open source.
Portable Adium is the multiprotocol instant messaging client that can connect to AIM, MSN, Jabber, Yahoo, and more, packaged as portable application so you can carry around with you on any portable device, USB thumb drive, iPod, portable hard drive, memory card, other portable device (also on your internal hard disk) as long as it has 65 MB of free space and use on any Mac OS X computer, taking your conctact list, emoticons, message stiles, plugins, scripts, sound and users with you.
So now you can take your favorite friends on the go anywhere you please and look more antisocial to the elderly(no offense), but you know the adverse is true.