PKZip.exe helps you unzip zipped files that you might download on the Internet. This version of PKZip is 2.63. It's an old version, but a good one. If you like it you can upgrade to the current version and pay some cash.
Since my PC recently crashed, I had to go find PKZip to unzip the preview of the new Blogging Book from O'Reilly: Essential Blogging. They put their book up on the web for free so we can review it for technical accuracy before it gets published.