OpenCart - A free shopping cart system. OpenCart is an open source PHP-based online e-commerce solution.s
WooCommerce - A freely available eCommerce plugin that enables shop facilities on your WordPress website. Functionality enabling extensions & beautiful themes available.
AbanteCart - Free, open source, shopping cart/ e-commerce platform.
Shopify - Shopify is a powerful ecommerce platform that includes everything you need to create an online store and sell online. Try it free for 14 days.
Zen Cart - Zen Cart
BigCommerce - BigCommerce provides ecommerce software solutions and shopping cart software for online businesses. Try it free and start selling your products online today!