ZK's biggest strength is its productivity. But it does have other advantages:
ZK decouples the rendering logic from the presentation logic. That means with ZK, applications can be retargetted to devices other than the browser, such as the desktop or Swing or even a mobile device.
Async update has always been an issue. With ZK the whole async update business can be abstracted into a timer component and it is very easy to do. However, you still have to pay attention to your server-side logic.
ZK's ZUML makes it easy to build complex UI component trees. It also shortens the edit—compile—test cycle for developers.
ZK allows developers to keep their business logic on the server side.
ZK is a ...