The Klarna-api-bundle PHP SDK by asgoodasnu is an SDK that integrates and wraps the Klarna API into a symfony2 bundle. The Klarna API allows developers to integrate Klarna's functionality with other applications. Some example API methods include emailing invoices, crediting invoices, calculating costs, and managing inventories.
The Web Payments Working Group has published the first public drafts of payment specifications which include a Payment Request API, payment method identifiers, and basic card payment. The basic idea behind the specifications is to make payments easier and more secure for end users.