The Rackspace PHP SDK is a development kit that lets developers integrate multiple different Rackspace APIs with their applications, using PHP. Some of the Rackspace services that this SDK supports include Cloud Files, Cloud Block Storage, and Cloud DNS.
FinancialForce.com, focused on building cloud based business applications on the Force.com platform, has released an API for its accounting application (i.e. The FinancialForce Accounting API). The API gives access to the entire suite of accounting tools available through the accounting platform (e.g. cash management, reporting and dashboards, ordering and billing, etc.). Although FinancialForce.com built the application with Force.com, and the target audience began with Force.com developers, the application has been integrated with many platforms and APIs (e.g. Google Apps, Basecamp, Facebook, PayPal, etc.)