Magento

The work of some of the most highly skilled programmers in the open source e-commerce community.

Drupal Commerce

A fast growing, flexible eCommerce framework based on Drupal.

WooComerce

Transform your WordPress website into a thorough-bred eCommerce store for free.

VirtueMart

eCommerce for smaller to mid-sized stores. Works with Joomla.

OpenCart

Attractive interface that is fairly simple to use with great built in SEO.

GoCart

Easy to customize. Easy to use. Built on CodeIgniter.