A library to interact with the Zotero API. This repository contains PHP and Python versions with similar interfaces. The PHP version sees limited use on zotero.org itself. The Python library is a nearly direct port of the PHP library.
Unfortunately, neither of these versions gets too much attention or maintenance currently.
If you're looking for the JS version, it is now maintained in a separate repository as it diverged significantly from the other versions. It is now at https://github.com/fcheslack/libZoteroJS