WooCommerce is an eCommerce plugin for the WordPress CMS. It is the most popular eCommerce software on the internet, used to power about 39% of all eCommerce websites at time of writing. It's greatest strength is it's ease of use for shop owners and high flexibility for developers allowing it to be moulded to suit a large variety of online stores. Most of the flexibility of WooCommerce comes from extensive use of the WordPress action and filter system and it's own template system which allows templates to be overridden in theme code.

WooCommerce is mostly developed by Automattic.

Open-Source

WooCommerce is open source software. You can contribute by making pull requests at it's github repository. Find out how to contribute here.

Documentation

The official WooCommerce documentation contains documentation for shop keepers administrating a WooCommerce powered website and developers who work with WooCommerce.