Square now has an E-commerce API that brings Square services to third party websites. Square is usually associated with its mobile credit card reader and complementary software. With the E-commerce API, merchants can use their own systems with all the benefit of Square's modern payment services.
The initial releases from credit card provider MasterCard look to be more than a toe-dip into APIs. With its MasterCard Payments API and two others, the company could be diving straight into the deep end. Though the services are still in beta, MasterCard appears to be taking very seriously its creation of a developer ecosystem.