osCommerce

osCommerce has attracted a large growing e-commerce community that consists of over 231,600 store owners and developers who support each other and extend osCommerce Online Merchant with add-ons being contributed on a daily basis. To date there are over 5,900 add-ons that are available for free to customize osCommerce Online Merchant online stores and to help increase sales.
osCommerce Online Merchant is an Open Source online shop e-commerce solution that is available for free under the GNU General Public License. It features a rich set of out-of-the-box online shopping cart functionality that allows store owners to setup, run, and maintain online stores with minimum effort and with no costs, fees, or limitations involved.
With over 8 years of operation, osCommerce has built a showcase of over 12,700 online shops that have been voluntarily added to the live shops section, and powers many thousands of more online shops worldwide.

Open Source

Open Source

http://www.oscommerce.com/