flexi cart is a shopping cart library for CodeIgniter. While CodeIgniter comes with its own cart library, the library is quite basic in functionality and is only aimed at creating simple e-commerce stores. The flexi cart library includes the following features: shipping, taxes, localisation, discounts and reward points/vouchers, multiple currencies, item stock control, surcharges, saving/loading of incomplete carts for later shopping, multilingual custom status and error messages, and currency and weight conversion tools.
Arcavias is an e-commerce framework for Web shops, consisting of an e-commerce library, an administration interface, and different frontends. It's a modular stack which offers flexibility and speed. Unlike other Web shops, it's not a monolithic application. Instead, you have a choice between several user frontends, and you can adapt them to your needs or write one of your own.
ZedCMS is a simple base content management system from which more complicated systems can be developed. It is designed so a Web developer can quickly produce customised websites, and is not really for users. Users wanting to setup their own websites are better off with a different system, like Wordpress.