Extract content from a pkg or mpkg "file"

Ever wondered what's inside a .pgk or .mpkg file?
In general they are directories so it can be accessed from the shell, or right-clicking it and choosing "Show Package Contents". The application data is packed in the file named: Archive.pax.gz.
To uncompress it:
   gunzip Archive.pax.gz
   pax -rvf Archive.pax

and voilà, behold all the package content unrolled before you.

I the right-clicking does not work then the .pkg is not a directory but a file. In this case there is a handy application named unpkg, that will just do the trick.


Sources:
http://en.wikipedia.org/wiki/Pax_(Unix)
http://www.linuxquestions.org/questions/linux-general-1/cant-extract-macosx10-4-universal-pkg-678167/
http://www.macupdate.com/app/mac/16357/unpkg