Zend Framework is a fully object-oriented framework, and as such, it utilizes a lot of object-oriented (OO) concepts like inheritance and interfaces. This makes most, if not all, of ZF's components extendable to some point. It allows developers to implement their own special variations of individual components without having to hack into the ZF codebase itself. Being able to customize ZF this way allows you to create functionality that is unique to your project, but because of its object-oriented nature, you'll be able to use this functionality in other projects as well. By design, Zend Framework is simply a collection of classes. Normally, you'll use Zend MVC components to create a fully-functional ZF project, but in any other case, you can just load the components you need. ZF is very decoupled, which means we can take advantage of the components as individual libraries, instead of the framework as a whole.
ZF, by default, is a glue framework. Its decoupled nature makes it easy to use as "glue" to your already existing application. The first development release of Zend Framework 2.0 was released on August 6, 2010. The first stable release of Zend Framework 2.0 was released 5 September, 2012
Zend Framework 2 is an open source framework for developing web applications and services using PHP 5.3+. Zend Framework 2 uses 100% object-oriented code and utilizes most of the new features of PHP 5.3, namely name spaces, late static binding, lambda functions and closures.
Zend Framework 2 evolved from Zend Framework 1, a successful PHP framework with over 15 million downloads.
The component structure of Zend Framework 2 is unique; each component is designed with few dependencies on other components. ZF2 follows the SOLID object oriented design principle. This loosely coupled architecture allows developers to use whichever components they want. We call this a “use-at-will” design. We support Pyrusand Composeras installation and dependency tracking mechanisms for the framework as a whole and for each component, further enhancing this design.