osCommerce

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.

Homepage: http://www.oscommerce.com/
Disk Space: 5.8 MB
Support Forum: http://forums.oscommerce.com/
License: GPL