Hazel
Hazel is a shopping cart written in C. A shopper clicks on links and submits forms which ask Hazel to add items to their order. Billing (and shipping) data is also entered and collected by Hazel. She computes the cost of the order and sends the information to the shopkeeper for processing. Sales tax, shipping, discounts and other order components are completely configurable by the shopkeeper via Hazel's "rules" files. Hazel also allows you complete freedom to design your site the way you see fit.