This is the official Shopify Ruby Gem that allows developers to programmatically access the admin functionality of Shopify stores. Developers can create apps for themselves through their own admin access. All API usage happens through Shopify applications; shop owners can create applications for themselves through their own admin. Developers are given functionality across articles, assets, customers, events and more. The API uses a RESTful interface and responses are formatted in XML and JSON.
Square is moving beyond the retail terminal thanks to a handful of new APIs meant to help companies accept payments in more places. The E-Commerce API and Register API target retailers large and small with a simple set of tools that integrate fully with Square's payment processing platform.