https://wincent.com/wiki/Uninstalling_packages_(.pkg_files)_on_Mac_OS_X describes how to uninstall .pkg using native
$ pkgutil --pkgs # list all installed packages
$ pkgutil --files the-package-name.pkg # list installed files
After visually inspecting the list of files you can do something like:
$ pkgutil --pkg-info the-package-name.pkg # check the location
$ cd / # assuming the package is rooted at /...
$ pkgutil --only-files --files the-package-name.pkg | tr '\n' '\0' | xargs -n 1 -0 sudo rm -f
$ pkgutil --only-dirs --files the-package-name.pkg | tail -r | tr '\n' '\0' | xargs -n 1 -0 sudo rmdir
Needless to say, extreme care should always be taken when removing files with root privileges. Particularly, be aware that some packages may update shared system components, so uninstalling them can actually break your system by removing a necessary component.
For smaller packages it is probably safer to just manually remove the files after visually inspecting the package file listing.
Apparently, there was once an
--unlink option available in
pkgutil, but as of Lion it is not mentioned in the man page. Perhaps it was removed because it was deemed too dangerous.
Once you've uninstalled the files, you can remove the receipt with:
$ sudo pkgutil --forget the-package-name.pkg