Zend Framework is an open-source, object-oriented web application framework for building dynamic web applications and services using PHP. It provides a set of reusable components and tools that enable developers to create web applications with robustness, modularity, and maintainability. Zend Framework follows the Model-View-Controller (MVC) architectural pattern, which separates the application logic into distinct layers.

Key features and aspects of Zend Framework include:

1. Modular Structure: Zend Framework encourages the development of modular applications by providing a collection of loosely coupled components. Developers can use only the components they need, resulting in efficient and optimized applications.
2. MVC Architecture: Zend Framework promotes the use of the MVC design pattern, where the application’s logic is divided into three main components: Models (data handling), Views (presentation), and Controllers (handling user requests).
3. Reusable Components: The framework includes a wide range of reusable components for tasks such as input validation, database access, authentication, caching, form handling, and more. These components can be used independently or combined to build complex applications.
4. Extensibility: Developers can extend and customize Zend Framework by creating their own components and integrating third-party libraries.
5. Zend Expressive: Zend Expressive is a microframework built on top of Zend Framework that allows developers to create minimalistic and performance-oriented applications.
6. Composer Integration: Zend Framework components can be installed and managed using Composer, a popular PHP package manager.
7. Zend Server: Zend Framework can be integrated with Zend Server, a PHP application server that provides tools for deploying, monitoring, and managing PHP applications.
8. Community and Documentation: Zend Framework has an active and supportive community that provides documentation, tutorials, and forums to assist developers in using the framework effectively.
9. Security Features: Zend Framework includes security measures like input filtering, output encoding, and encryption to help developers build secure applications.
10. RESTful Services: Zend Framework provides tools and components to create RESTful APIs and web services.
11. Integration with Other Technologies: Zend Framework can be integrated with various web services, databases, and third-party APIs.
12. Zend Framework and Laminas: In 2019, the Zend Framework project transitioned to become the Laminas Project. Laminas is a continuation of Zend Framework with a focus on providing a set of components for building applications, rather than a full-stack framework. Existing Zend Framework components can still be used in Laminas applications.

Zend Framework has been used to develop a wide range of web applications, from simple websites to complex enterprise-level applications. It offers developers the flexibility to create applications tailored to their specific needs while benefiting from a rich collection of tools and components.