WooCommerce - A freely available eCommerce plugin that enables shop facilities on your WordPress website. Functionality enabling extensions & beautiful themes available.
Sitecake - Drag and drop CMS for HTML websites. It's flat file CMS so it's pretty fast.
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.
Anchor CMS - Free and lightweight blogging system
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.
Textpattern - Textpattern is an elegant content management system that is free, open source software.