OpenCart - A free shopping cart system. OpenCart is an open source PHP-based online e-commerce solution.s
Skuuudle - Discover, match and monitor your eCommerce competitors.
WooCommerce - A freely available eCommerce plugin that enables shop facilities on your WordPress website. Functionality enabling extensions & beautiful themes available.
Price2Spy - Price2Spy is a price monitoring, pricing analytics, and repricing tool, meant to help eCommerce professionals keep an eye on their competitors or retailers.
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.
BuiltWith - Find out the technology behind websites