eCommerce

PHP

Magento

Spree (Ruby on Rails)

Seotoaster

PrestaShop
OpenCart
http://www.ubercart.org
http://www.zen-cart.com
http://www.oscommerce.com

Extensions CMS

WordPress
http://getshopped.org e-Commerce

Joomla
http://extensions.joomla.org/extensions/e-commerce VirtueMart
http://extensions.joomla.org/extensions/extension-specific/virtuemart-extensions
http://virtuemart.net

Drupal
http://drupal.org/project/ubercart Ubercart
http://www.drupalcommerce.org Drupal Commerce

MODx
http://modx.com/extras/package/visioncart VisionCart
http://modx.com/extras/category/e-commerce

SilverStripe
http://code.google.com/p/silverstripe-ecommerce eCommerce
http://www.silverstripe.org/silvercart-module SilverCart

Discussion

http://godropship.com/Forget-Magento.-Wordpress-Can-Power-Your-Ecommerce-Store.html

http://techetips.com/top-ten-open-source-e-commerce-shopping-cart-software

http://php.opensourcecms.com/scripts/show.php?catid=3&sortby=rate asc eCommerce
http://www.hongkiat.com/blog/setting-up-your-first-online-shophttp://www.sitepoint.com/the-world-of-ecommerce-solutions-simplified-for-your-business/#post-52343
http://www.cmscritic.com/hippo-teams-with-commercetools-to-bring-relevant-content-rich-ecommerce-experiences

http://www.hongkiat.com/blog/basic-ecommerce-tips

https://ecommerce-platforms.com/articles/open-source-ecommerce-platforms

SaaS

http://www.sitepoint.com/more-hosted-shopping-carts-bigcommerce-and-volusion
http://www.sitepoint.com/10-best-self-hosted-ecommerce-solutions
https://shopify.com