osCommerce -- Open Source E-Commerce Solutions

"osCommerce is an online shop e-commerce solution under on going development by the open source community. Its feature packed out-of-the-box installation allows store owners to setup, run, and maintain their online stores with minimum effort and with absolutely no costs or license fees involved.

osCommerce combines open source solutions to provide a free and open e-commerce platform, which includes the powerful PHP web scripting language, the stable Apache web server, and the fast MySQL database server.

With no restrictions or special requirements, osCommerce is able to run on any PHP enabled web server, on any environment that PHP and MySQL supports, which includes Linux, Solaris, BSD, Mac OS X, and Microsoft Windows environments."

Via this post from Marcus P. Zillman.