Lostfiles is a script for detecting orphaned files (files which are not owned by any Arch Linux packages).
An AUR package has been created for easy and convenience:AUR
The script generates a list of all files owned by installed packages and compares that against all files on the root filesystem showing the user the difference, i.e. files on the filesystem that are not owned by a package. Users can inspect the output and choose to leave any orphans alone or to backup and delete them.