Recently all my E Commerce Websites have been done with WordPress, Joomla or Silverstripe. They are NOT REALLY designed as e commerce but with the right plugins (such as WooComerce for WordPress or Virtuemart for Joomla) they can easily be set up as fully functional E Commerce Websites with or without Shopping Cart and with various Payment Modules such as PayPal, Direct Bank Deposit or others.
But Zen Cart (demo here) is actually THE E-Commerce/Shopping Cart System. Free to download, super support, lots of free and commercial themes to choose from.
You just cannot go wrong if you want to set up a pure Shopping Site where you basically need Product Categories, Product Attributes (color, size etc) and of course Products.
Various Payment Modules come pre installed, others can be added.
One of my very first (and now very busy) Zen Cart Shop has been The Letterlady an Online Shop selling handmade wooden cut outs for Children’s Bedrooms and other Decorations.
Zen Cart is an Open Source web application that is truly an art of E commerce and a user-friendly open source shopping cart software. It is an online store management system based on PHP & which has some very good advantages like- automated tasks, simplified navigation, supporting multiple languages & also it keeps a complete record of all the online sales. Zen Cart assists the online shopping management with very good interactive applications development.