I get a lot of people hit me up saying "Dude, I see you online on Facebook all the time, do you ever do any work?", little do they know I'm actually using chat clients to plug in to Facebook Chat without actually needing to be on the site. A lot of people don't realize that they can use Facebook Chat just like MSN or Google Talk, so I thought I'd give a quick rundown of what's available.
Pidgin (Windows and Linux)
Pidgin is an Opensource chat client which can aggregate multiple chat systems into the one program, this means that you can use it plug in to MSN, Google Talk, Yahoo Chat, AIM, Bonjour and other popular chat systems all in the one program. Facebook chat will require a simple plugin to get it working, but once thats on there you can chat to all your friends on Facebook in a much better interface than what's available on the site.
You can download Pidgin from: www.pidgin.im
The Facebook plugin can be found here.
Adium (Mac OS X only)
Adium pretty much is just Pidgin, except it's build to utilize the goodness of Mac OS X, this means that you get cool things like Growl notifications, and icons jumping on the dock bar (you better envy that stuff Windows users). The sweet thing with Adium though is that it comes packaged with Facebook Chat, so you're all good to go once it's installed. In my opinion Adium has a much better interface than iChat and much easier to use.
Adium can be downloaded from: www.adium.im
Digsby (Windows only. Linux and Mac coming soon)
Digsby is designed to be a one-stop-shop for emails, chat and social networking. It can give you email alerts, use all the popular chat systems (including Facebook Chat) and also let you manage your Facebook and Twitter accounts, all from the one tool. In my opinion I found the interface very messy and difficult to work with, as well as an issue where the system would momentarily disconnect from the chat servers, which was a pain in the ass in the middle of a conversation. It also didn't provide adequate alerts when someone was trying to contact me on chat, so I had a few cases where people thought I was ignoring them.
Even though I wouldn't recommend it, digsby can be found here: www.digsby.com
Gabtastik (Windows and Mac OS X)
This is called a "Site Specific Browser" designed to let you have Facebook chat running in another window. This seems to be no different from clicking "pop-out chat" on Facebook, so there's really no point in downloading this, as it's kind of a waste of time.
If you do want to find out more you can visit: www.gabtastik.com
As I do work in three different Operating Systems (Ubuntu 9.04, Mac OS X Leopard and Windows XP), I find Adium on Mac, and Pidgin on Windows and Linux have the best user interface and the most reliable.