Vaadin vs ZK: What are the differences?

### Introduction

1. Architecture: Vaadin supports server-side architecture where the UI components are generated on the server and sent to the client. In contrast, ZK uses a client-server architecture where the UI components are created and managed on the client-side. This difference affects how the UI is rendered and the level of control developers have over the components.

2. Component Model: Vaadin offers a more Java-centric approach with a rich set of pre-built Java components, making it easier for Java developers to work with. On the other hand, ZK provides a more XML-centric approach, allowing developers to define UI components using XML tags, which can be more intuitive for web developers familiar with HTML.

3. Event Handling: In Vaadin, event handling is mainly done on the server-side, where the client sends events to the server for processing and reacting to user actions. ZK, however, supports both server-side and client-side event handling, giving developers more flexibility in choosing where to handle events based on performance and scalability needs.

4. Theming and Styling: Vaadin provides a theming mechanism that allows developers to customize the look and feel of components through CSS and predefined themes. ZK, on the other hand, offers a more versatile skinning mechanism that includes themes, templates, and dynamic styles, giving developers more control over the visual aspects of their applications.

5. Mobile Support: Vaadin comes with built-in responsive design features that enable applications to adapt to different screen sizes and devices out-of-the-box. In comparison, ZK provides a separate library called ZK for Mobile that focuses on creating mobile-friendly user interfaces, offering a more specialized approach for mobile app development.

6. Community and Ecosystem: Vaadin has a large and active community with a range of add-ons, extensions, and third-party integrations available, providing plenty of resources and support for developers. Although ZK has a smaller community, it offers enterprise-level support and solutions, making it a preferred choice for organizations looking for comprehensive support and documentation.

### Summary

In Summary, Vaadin and ZK differ in architecture, component model, event handling, theming, mobile support, and community ecosystem, catering to different developer preferences and application requirements.