Zipper is a tool for inspecting the contents of a compressed archive and for extracting.
I know that there's a GNUstep port of the famous OpenUp application but I must admit that for a living I have to use Windoze at work.
After a while I got quite used to Winzip's UI. Although I don't like some of its features, what I really like is the content listing of an archive without actually having to unpack it. This is what Zipper currently tries to mimic.
This has also the advantage that you don't have to unpack archives from networked volumes to your local disk just to view what's in it.