ZK assumes nothing about persistence or inter-server communication. ZK is designed to be as thin as possible. It is only aimed at the presentation tier. It does not require or suggest any other back-end technologies. All of your favorite middleware technologies such as: JDBC, Hibernate, Java Mail, EJB or JMS work as they used to.

ZK doesn't provide a tunnel, RMI or other API for developers to communicate between clients and servers. This is because all code runs at the server within the same JVM.

ZK doesn't enforce developers to use MVC or other design patterns. Whether to use them is the developer's choice.

ZK is not a framework aiming to bring XUL to Web applications. It is aimed to bring the desktop programming model to Web applications. Currently, it supports XUL and XHTML, in future it might support XAML, XQuery and others.

ZK embeds AJAX in the current implementation but it doesn't end in where AJAX does. With ZK API for Mobile devices, your applications could reach any devices that support J2ME such as: PDA, mobiles and game consoles. Moreover, you don't need to modify your application at all^[7].