osCommerce or “open-source Commerce” is an e-commerce and online store-management softwareprogram. It can be used on any web server that has PHP and MySQL installed. It is available as free software under the GNU. osCommerce’s online merchant platform is a comprehensive PHP-based ecommerce solution for online retailers.  Think of it as the grandfather of all open-source shopping carts. Zen Cart is actually a branch off of the osCommerce software.