Magento is a fairly recent additions to the Open Source Shopping Cart Software scene but has been developed for quite some time and is now in past its first production release v1.
Magento Commerce by their own description:
“Magento is the eCommerce software platform for growth that promises to revolutionize the industry. Its modular architecture and unprecedented flexibility means your business is no longer constrained by your eCommerce platform. Magento is total control. “