Add-ins and Extensibility
Add-ins provide extended features or services for a host application. The .NET Framework provides a programming model that developers can use to develop add-ins and activate them in their host application. The model achieves this by constructing a communication pipeline between the host and the add-in. The model is implemented by using the types in the System.AddIn, System.AddIn.Hosting, System.AddIn.Pipeline, and System.AddIn.Contract namespaces.
For additional code samples, and customer technology previews of tools for building add-in pipelines, see the Managed Extensibility and Add-In Framework site on CodePlex.