OpenPetLocator is a free implementation of a pet search engine tool to allow shelters to publish their animals to a central site and allow potential owners to find by proximity. Similar to PetFinder. It's currently used to power FindMeAPet.com.
Features automatic signup emails, FTP interface/indexing tool and a fully internationalised PHP frontend.
Requires PHP, Apache, MySQL, ImageMagick (and optionally, Python and FTPD)