From Cibernética Americana
E Commerce and other Integrations and Customizations
You may want to have a package such as Magento, osCommerce, etc. integrated into your app. This can be done and in such a manner that visitors to your site will see it as seamless. However the integration of these packages will be superficial and this will be apparent to you in backend. VirtueMart is free but requires Joomla/Mambo. Volusion is not open source software but rather a priced service like PayPal, Amazon, etc.
I'm developing an advanced integrative framework but he integration addressed here is simply to make the front end apply correct transactions to loosely coupled backend systems.
This module was removed from the d.o repo due to a security concern which I can address if you wish to use this package.
Ubercart in d7
Learned relation of d6 eCommerce / d7 / UC earlier this year (2011), Cliu is using community edition of Magento for this function.
E commerce 2013-Q2
Using the 'standard' commerce modules in d7, this stuff is larger superceded in intent if not function with the interface to the ledger based dominion stuff.