Firewall Add-in/Plug-in

I've been hearing from some of my friends and fellow techies about firewall add-ins or plug-ins, but haven't found any myself, despite some searches on Google. Perhaps I'm looking for the wrong thing, but I can't find it!

I run WinXP and have a Sygate Firewall running, which stealths all my ports. Does anyone know what these add-ins do, or if they're any good? Are they needed with a good firewall already running?

Do they even exist? My friends could have been confused and talking about something else (i.e. proxies) but insist that they are not.

Any insights?

The only firewall I can think of off the top of my head that actually allows for the creation of plugins is Agnitum Outpost. If your firewall is properly configured and stealths all your ports, then I can't really see the need for anything extra to be installed, because after all, the more you have installed, the more potential holes you could have. The only possible useful plugins I could think of would be like an IDS if your firewall doesn't already have one built in, or perhaps some kind of log utility to make them searchable or easy to print and read?

Sygate has VERY good logging, easy to read and print. Just making sure that I didn't misunderstand something completely.

I don't think it's a plug in but visual zone has a free add on for zone alarm which has an whosis and other features which it uses when it imports the za logs