cpCommerce is an open-source e-commerce solution that is maintained by templates and modules.
This Ecommerce Script combines many utilities found in other "free" ecommerce scripts, except I allow you to completely customize the entire design by editing a single template file and the CSS (Cascading StyleSheets) each section pertains to. Due to how the script was developed, the program finds your template, and is told where to place each element in the program using easy to read tags.
Some of the basic necessities needed to run cpCommerce is a web server that is both PHP and MySQL enabled and you will need at least 5 MB of storage. You can read a much more detailed list at the Server Requirements page.
Go to http://cpcommerce.cpradio.org/
See also these related projects.