[modi123_1]

http://net.tutsplus....s-with-add-ons/

A pretty boss tutorial to learn how to make your apps accept "add ons". This is not for the novice, but there are excellent concepts to see in action.

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Your application lacks a cool whizbang feature? Let other interested developers extend your application through add-ons. By opening up your app to additional functionality down the line, you can build a thriving community around your application, potentially even a marketplace!

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We’re going to build a proof-of-concept application that, upon start-up, loads add-ons that it finds in one of its subdirectories. These add-ons are .NET assemblies that contain at least one class which implements a particular interface as defined by us.

[AdamSpeight2008]

Also you can consider using MEF in .net4