GitHub is a great source of third-party add-ons. A lot of Odoo partners use GitHub to share the add-ons they maintain internally, and the Odoo Community Association (OCA) collectively maintains several hundred add-ons on GitHub. Before you start writing your own add-on, ensure that you check that nothing already exists that you can use as is or as a starting point.

This recipe will show you how to clone the partner-contact project of the OCA from GitHub and make the add-on modules it contains available in your instance.