Is ZF a component library or a framework?
Both. Zend Framework provides all the components required for most web applications in a single distribution. But Zend Framework components are also loosely coupled, making it easier to use just a few components to provide functionality to a web application- even alongside other frameworks! With this use-at-will architecture we are implementing features commonly found in more monolithic frameworks. In fact, we are currently working on a tooling component that will make it simpler to build applications using ZF components, yet will not sacrifice the use-at-will nature of existing ZF components. In fact, the tooling component itself can be used alone.
