The Google Shopping Content Objective-C Library by Google can access API data to sell products on Google, list ads, drive traffic, and increase sales. Developers can interact with the JSON API, working with iOS 3+ and Mac OS X 10.5+. Available introduction and example applications.
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.