osCommerce!

Summary:
osCommerce is an online-based Open Source e-commerce solution that is available for free under the GNU General Public License. It was started in March 2000 in Germany by project founder and leader Harald Ponce de Leon as The Exchange Project. It can be used on any web server that has PHP and MySQL installed.

osCommerce features a rich set of out-of-the-box online shopping cart functionality that allows store owners to setup, run, and maintain their online stores with minimum effort and with no costs, fees, or limitations involved. While officially osCommerce is still in its development stage, the current Milestone 2.2 release is considered stable. As of November 2007 the osCommerce site says that there are over 12,000 'live' websites using the program.

Source
osCommerce
http://www.oscommerce.com/

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News References
OsCommerce News
http://www.openpr.com/news/17064/OsCommerce-News.html

PayCash Implements osCommerce Module
http://www.cyphermint.com/news/2004_11_10_oscommerce.html

Store Manager for osCommerce
http://www.magneticone.com/PAGE-56-oscommerce-store-product-manager.html