A tool that recursively walks filetrees and store paths + sha1 in a database
You will be able to use this database to query all kinds of information out of it. For example, duplicate files, or files that exist in one directory and not in the other.
Instructions on how to use the directory-scanner utility on your Mac are available HERE.
directory-scanner is cross-platform and it works on Mac OS X, Windows and Linux. Binaries for the Windows and Linux platforms are available on the project's homepage.