WordPress E-Commerce Plugin
Jigoshop - a WordPress eCommerce plugin which works. It is free to download and install, and comes with everything you need to create an online store.
Flexible eCommerce solutions, a vibrant extensions marketplace and an open global ecosystem
Open-source eCommerce solution. nopCommerce is available for free. It has everything you need to get started in selling physical and digital goods over the internet.
PrestaShop is a free ecommerce solution powering over 200,000 online stores. We tweet and live for online retail, Open source, free software and web culture.
Shopify is a commerce platform that allows anyone to easily sell online, in-store, and everywhere in between. Preferred by over 100,000 merchants worldwide.
Zen Cart truly is the art of e-commerce; free, user-friendly, open source shopping cart software.