OpenCart - A free shopping cart system. OpenCart is an open source PHP-based online e-commerce solution.s
PrestaShop - Create your online store with PrestaShop's free shopping cart software. Build an ecommerce website for free and start selling online with hundreds of powerful features.
WooCommerce - A freely available eCommerce plugin that enables shop facilities on your WordPress website. Functionality enabling extensions & beautiful themes available.
1ShoppingCart - 1ShoppingCart is an online store software to build a secure eCommerce storefront.
Zen Cart - Zen Cart
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.