OpenCart is an open source PHP-based online shopping cart system. A robust e-commerce solution for Internet merchants with the ability to create their own online business and participate in e-commerce at a minimal cost.
OpenCart is designed feature rich, easy to use, search engine friendly and with a visually appealing interface.
Yoga online
Magento is also free and it works fine, There’s a lot of info about Magento around the net.
eRage webdesign
I’ve been using OpenCart for quite some time now, it’s excellent software! Magento is way too big for me.