Zend is a popular open-source framework for developing web applications and services using the PHP programming language. It provides a collection of reusable components and tools that help developers create robust and scalable applications efficiently. Originally released in 2006, Zend has evolved to support modern web development practices, including MVC architecture and RESTful APIs. The framework is maintained by Zend Technologies, which also offers commercial products and services to enhance the development experience, such as the Zend Server for application deployment and management.