CAB Resource

The Composite UI Application Block, created by Microsoft's patterns & practices team, is a reusable, source code–based component based on the Microsoft .NET Framework 2.0.
It provides proven practices to build complex smart client user interfaces based on well known design patterns such as the Composite pattern, in which simple user interface parts can be combined to create complex solutions, but at the same time allowing these parts to be independently developed, tested, and deployed.
In other words, it separates UI related logic and the business logic behind it to separate classes, making it easier to test and refactor you BL code without touching the UI and the other way around.
As it turns out, there is a WIKI resource on the subject, called CABpedia.