Symfony is a set of reusable PHP components and a PHP framework for web projects. It Speeds up the creation and maintenance of your PHP web applications and Ends repetitive coding tasks and enjoy the power of controlling your code.
Yii is a free, open-source, PHP framework best for developing both web applications and APIs. It comes with rich features: MVC, DAO/ActiveRecord, I18N/L10N, caching, authentication and role-based access control, scaffolding, testing, etc.
Zend Framework is an open source framework for developing web applications and services using PHP. Zend Framework uses 100% object-oriented code and utilises most of the features of PHP, namely namespaces, late static binding, lambda functions and closures.