Leading Open Source eCommerce software
Magento: Magento is the gorilla of the open source e-commerce market. It is providing many of the features you are waiting from a modem e-commerce platform: Advanced Catalog & Order Management, tagging, voting, social networking, SEO compliance…. A Must See solution.
Sylius: Sylius is an Open Source Headless eCommerce Platform for mid-market and enterprise brands that need custom solutions. It is based on PHP Symfony framework
Drupal Commerce: Drupal Commerce is a lean open source e-commerce framework built on Drupal 7. Use it to build flexible and highly customizable websites for social commerce.
Other Open Source eCommerce software
PrestaShop: PrestaShop is professional open source eCommerce shopping cart software. Pretty newcomer, it is competing against Magento in the full-featured open source e-commerce suite.
Solidus: Solidus offers a complete suite of essential eCommerce features out of the box in a fully modular package. It is based on Ruby on Rails.