epacke[k] is a gui for gunzip and pax Osx commands.

This tool can load a compatible .pkg (made with apple´s packagemaker), locate the file archive.paz.gz (where the contents are) and decompress them in it´s original folder tree, allowing you to:
1.Unpace in place an audio plugin, then recreate again the package.
2.Replace a cracked file on the installer and rebuild the installer.
3.Take a look inside the package before you install it to know what are you installing.