Great question — answering as the UphillTech team:
Sure, nopCommerce . From their Overview page: nopCommerce is a fully customizable shopping cart. It's stable and highly usable. nopCommerce is an open source e-commerce solution that is ASP.NET 3.5 based with a MS SQL 2005 (or higher) backend database.
Full answer by luvieere: https://stackoverflow.stackexchange.com/a/1584660 (CC BY-SA 2.5).
Need it done for your business? UphillTech.