The Composite UI Application Block (CAB) is an interesting architectural solution for smart client development. It is essentially a plug-in architecture that brings the WebParts concept to the desktop.

The CAB has the following elements:

• WorkItems. These are the classes which represent use cases in your application and contain the business logic for those use cases.
• SmartParts. There are the building blocks of a Windows-based application - similar in concept to WebParts.
• Workspaces. These are helper classes that can display SmartParts with a uniform style.
• UIElements. These are elements such as toolbars and menu bars that are shared by SmartParts within the application.
• Support services. These include:
  • Event broker service to manage the publishing and subscribing of events between SmartParts.
  • State management service to hold shared state for areas within the application. This provides an option to encrypt the state before it is stored.

The CTP is now available on GotDotNet (needs .NET 2 beta)