The xTuple Point of Sales (xtPOS) system is an extension package that can be run on any edition of xTuple ERP (including the free PostBooks Edition) to add Point of Sale / Cash Register capabilities to the software.
Here's a comparison of the functionality you'll find in xTuple's products. Blue hyperlinks will take you to a Flash video or additional documentation on that particular subject. Costs for licenses, service and support are covered on our pricing page.