Jolicloud is a stripped down operating system that, instead of running software, connects to Web services using their application programming interface (API).

FORBES: The Disposable Operating System

Bug-for-bug compatibility is a problem, but breaking backward compatibility would be a much bigger problem, so even as the lowest layers of the operating system are revised and rewritten, the layers that applictions talk to (the application programming interface, or API) are carefully tested to ensure that no changes are visible to the application.

FORBES: What Is So Great About Microsoft?

The state of the art in this model of programming is Pegasystems, which is often called a BPM system but is really a declarative application development environment.

FORBES: A New Open-Source Model For SaaS