nopCommerce is an open source eCommerce platform build in ASP.NET MVC as a frontend and MS SQL as a backend for database.
nopCommerce was launched in October 2008. It is available under Public License V3.
nopCommerce is a safe, extandable and scalable eCommerce solution with Administration options for managing frontend catalog, customers, wish lists and discount coupons. It has support of most popular payment gateways like PayPal, Google Checkout, Authorize.net and many more.
Since its open source you can grab your free copy of nopCommerce source code from here.