WooCommerce - A freely available eCommerce plugin that enables shop facilities on your WordPress website. Functionality enabling extensions & beautiful themes available.
Beyond Compare - Beyond Compare allows you to compare files and folders.
PrestaShop - Create your online store with PrestaShop's free shopping cart software. Build an ecommerce website for free and start selling online with hundreds of powerful features.
WinMerge - WinMerge is an open source differencing and merging tool for Windows.
Shopify - Shopify is a powerful ecommerce platform that includes everything you need to create an online store and sell online. Try it free for 14 days.
Meld - What is Meld? Meld is a visual diff and merge tool targeted at developers.