Pkg Viewer [ macOS ]

If you are referring to standard Apple installer files, you do not need a special "viewer" app. You can use the built-in option in the macOS installer to see what will be installed before you run it. Alternatively, the command-line tool pkgutil --expand file.pkg output_folder can be used to unpack them.

Are you using this specifically for or for macOS application management? How to Backup your Installed PS4 App Pkg's to a USB on 9.00 PKG Viewer