osCommerce

From the official osCommerce website:

osCommerce is the leading 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 their online stores with minimum effort and with no costs, license fees, or limitations involved.

The goal of the osCommerce project is to continually evolve by attracting a community that supports the ongoing development of the project at its core level and extensively through contributions to provide additional functionality to the already existing rich feature set.

Everything you need to get started in selling physical and digital goods over the internet, from the Catalog frontend that is presented to your customers, to the Administration Tool backend that completely handles your products, customers, orders, and online store data.

To learn more about osCommerce you can visit the official website here: http://www.oscommerce.com/

Wallanet has set up a demo version of osCommerce so you can try it out. We've included access to the admin interface as well.

The demo version can be found here: http://demo.wallanet.com/oscommerce

You can login to the admin panel for this package by going here:
http://demo.wallanet.com/oscommerce/admin
Username: demo
Password: demo

To learn more about this e-commerce solution and all the other e-commerce solutions that Wallanet offers go here: http://www.wallanet.com/open_source_packages/e_commerce