Pacifist has an attractive, easy-to-use interface.
Pacifist can search all the installer receipts on your system to determine what package, if any, installed a given file. If the original packages can be found, Pacifist can extract the files from the packages.
If a file cannot be extracted via the Search Receipts feature, Pacifist can open a package and allow you to extract files from it manually.
Pacifist can open packages and several other archive types directly over the World Wide Web.
Pacifist can scan your hard disk for the files contained in a package, and notify you of any files which are missing or changed.
Finally, Pacifist can scan your Extensions folder and reveal which kernel extensions come from Apple, and which come from third parties.