[VB.Net] Building a modular/pluggable web application

We're aiming to build a modular/pluggable web application with the following structure:

* Core Web App: top-level MasterPage, BasePage, BaseControl, Authentication/Authorization, Shared Components: CSS, Images, JavaScript libraries, Common ASCX/Server Controls, etc

* Module/Plug-in 1: ASPX Pages (and code behind), sub MasterPage, Private Components: css/images/javascript, ASCX controls, etc

* Module/Plug-in 2: ASPX Pages (and code behind), sub MasterPage, Private Components: css/images/javascript, ASCX controls, etc

In this case, the core application has a set of classes and resources that all plug-ins will depend on, but the core does not depend on any of the plug-ins.

Each module/plug-in is a separate mini application unto its own, rather than a discrete module meant for placing on any chosen page. It will have its own internal structure and relationships, yet be housed within the core application.

For example, if you have a site like this: http://mysite/

Then, plug-in 1 should be accessed via http://mysite/Plug-in1, and any functions therein by http://mysite/Plug-in/Function1.aspx ... etc etc

If we were to implement this in a single-solution / Web Application Project, by putting each plug-in in its own folder, the code would all compile into one web application DLL that will need to be deployed. And that's not what we're looking for, because the plug-ins are meant to be optional extensions to the core application.

We want to be able to distribute the core application, and easily add plug-ins to it lateron.

Any ideas how to go about this?