OS/GPL eCommerce/ShopFramework for RoR?

Hi,
did someone knows a Shop or eCommerce Framework for RoR which is
available under GPL license or an additional CMS framework which can
be use for such an approach (I need such a framework for my master
thesis).
It would be nice if someone could mention such a framework if he knows
such a thing :).
Thanks in advance & best wishes,
Knut