osCommerce is a CMS for online stores. Can be hosted on your server or can create your online store directly on osCommerce website.
First time was developed in 2000 and now thousands of shopping sites are using this content management system.
Is based on PHP and MySql technologies, is easy to install and use. Features front-end interface (store itself) and administration area.
Thousands of add-ons are available to change or enhance functionality as you need (different types of online payments, send newsletters, management of images, languages, shipping etc.).
A large community is available to help and to explore more subjects.