UberCart is an open source shopping cart software which works integrated together with Drupal CMS/Social Portal Software and has been developed for quite some time and is now available in version 2.X.
UberCart by their own description:
“Ubercart is an exciting open source e-commerce package that fully integrates your online store with Drupal, the leading open source content management system. This is a killer combination for anyone looking to build a community around a product, sell access to premium content, offer paid file downloads, and much much more!
Ubercart was designed to take advantage of Drupal’s major core and contributed systems, providing our users with shopping cart functionality that seamlessly integrates with other parts of your company or community website. “