John,

>I have developed an application for clientA. Recently, I just get a call from clientB asking for the same application, however he wants some customization/enhancement.
>My question is, how could I subclass my application, that can reuse my code and easier maintenance?

You could create a new project that contains all the source code in your original project. Then, whenever you need to customize something for client B, you could create a subclass of an existing class. As an alternative, you COULD keep a single project and use the MM VFP Factory object to data drive instantiation of classes where functionality differs for Client A and Client B.

Regards,