Methods and apparatus, including computer program products, implement techniques for structuring applications into reusable components. A reusable software component is implemented. The component encapsulates functionality, where multiple instances of the component are usable at the same time. The component has at least one visual representation. The component has a programming interface for programmatic interaction with the component, a data-binding interface for data communication with the component, and a visual interface to access the at least one visual representation of the component.