Lostfiles is a script for detecting orphaned files (files which are not owned by any ArchLinux packages).
The script ignores by default a series of directories where packages should not install files. Some files might appear as removed if they're placed in those directories which are not checked (for example, some packages install files in /tmp - didn't have time to track which of them).
The latest version of the script can be found here: http://mircea.bardac.net/archlinux/tools/lostfiles
The script must be run as root.
Typical usage & output:
./lostfiles > changes Loading registered files... Finding local files... Finding local directories... Finding local links... Done.
- changes is a file containing a list of added/removed files
- "Loading registered files..." - doesn't take time, since pacman's DB is used
- "Finding local *..." - takes longer, since the script uses find to look for all the installed files
Assuming you have some application with a custom installer for which you don't know (yet) how to make a PKGBUILD. You could create a snapshot of the filesystems before and one after. Making a diff between the two snapshots will reveal the changes in the files (added/removed files) which occured during the install.