A Zip file is a compressed archive file used to make large files and collections of files more manageable to the user. When a.zip file is created, data is compressed to reduce the file size. Multiple files can be combined into a single Zip folder, making it easier to upload, download or email a volume of files. Most of the time unzipping a zip file in Windows is straightforward, but once in a while a zip file comes along and is nothing but trouble. With that in mind, today’s SuperUser Q&A post comes to the rescue to help a reader get a stubborn zip file opened. Third-Party Apps for Zipping and Unzipping Mac Files. The built-in compression system that can zip and unzip files in macOS and OS X is relatively basic, which is why many third-party apps are also available. A quick look at the Mac App Store reveals more than 50 apps for zipping and unzipping files. Zip Files for Mac; RAR Files for Mac. WinZip Mac 8 Pro. WinZip is the world's #1 choice when working with large files – zip, unzip, protect, share and more.