OpenCart - A free shopping cart system. OpenCart is an open source PHP-based online e-commerce solution.s

Selz - Seriously Simple Selling

WooCommerce - A freely available eCommerce plugin that enables shop facilities on your WordPress website. Functionality enabling extensions & beautiful themes available.

PayKickstart - PayKickstart is the ultimate shopping cart and affiliate management platform, empowering online Entrepreneurs and digital publishers with the tools to sell their products online.

WCFM Marketplace - WCFM Marketplace is a plugin made for WordPress that provides features for a multi-vendor marketplace platform.

Shopio - Shopio is an all-in-one hosted shopping cart solution.