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?