Magento

Beginning with its first beta versions in 2007, this tool, driven by US based Magento Inc. (formerly Varien), generated tremendous buzz worldwide, which allowed it to bring together an extremely active community in record time.

Magento's great strength lies in its superior modularity and its robustness. It was clearly devised to support ambitious, large scale merchant sites with functionalities like advanced categorisation, the definition of product groups, management of configurable products, cross-selling and up-selling functions, a powerful promotional engine, multi-shop management, advanced currency and VAT rate management, etc.
Initially distributed exclusively under the OSL, Magento's gamble paid off upon its release, capturing a large share of the market. In April 2009, Magento announced the release of an Enterprise edition. In return for an annual fee, this version provides a number of additional functionalities and a support contract.
The solution is based on the Zend PHP framework and boasts many innovations in terms of participatory functionalities.