WooCommerce - A freely available eCommerce plugin that enables shop facilities on your WordPress website. Functionality enabling extensions & beautiful themes available.
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OpenCart - A free shopping cart system. OpenCart is an open source PHP-based online e-commerce solution.s
Swell.is - Customizable, API-first ecommerce platform for innovative brands, startups, and agencies.
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.
Jumpseller - Start Your Online Store! Grow your business.