"Pacifist is a shareware application that opens Mac OS X .pkg package files, .dmg disk images, and .zip, .tar, .tar.gz, .tar.bz2, and .xar archives and allows you to extract individual files and folders out of them."
This tool is around since the early, I mean very early, days of OS X. It allows you to pop in your OS X installation disc and install files you accidentally deleted. (Fonts for instance because you were trying to save disk space …)
New in Pacifist 3 is the support for OS X Lion’s installer packages.