Released in April 2010
What is it
Opencart has a great order management, multiple ways of payment and shipping embedded in the system, it is possible to extend its functionalities through extensions (plugins or addons), and customize it's appearance through templates.
OpenCart was developed to be light and fast, it has a simplified and intuitive administration interface and a store structure that not only has a information cache system to speed up the loading of information, but it uses in a mature way the Jquery library in several resources, so that it loads information without the need to update the pages. Another strong feature is that it already comes with friendly URL's and SEO support.
Oficial Site: http://www.opencart.com/