osCommerce

osCommerce is the leading Open Source online shop e-commerce solution that is powered by a dedicated, strong, and ever growing community, and is released under the GNU General Public License.

Zen Cart

Zen Cart is the art of e-commerce; free, user-friendly, open source shopping cart software. The ecommerce web site design program is being developed by a group of like-minded shop owners, programmers, designers, and consultants that think ecommerce web design could be and should be done differently.

X-Cart

Shopping cart software trusted by thousands of successful business owners worldwide.