We have our own self-hosted shopping cart application that we have been using for our own eCommerce websites for more than 20 years! It’s written in C# using .Net MVC EF and MS SQL databases, so it is an industrial strength solution if you are going to be on an .Net platform. The standard category and product based version requires about the same setup time as any of the commercial and open source carts. RawrCart™ might be your best choice if you need a highly customized checkout process or any special functions in the order process that are outside the scope of what is available “off the shelf.” Completely customizable!