A common problem that developers face when building applications is how to allow the application to be "plug-able" at runtime.  Meaning, to allow non-core code to modify the way an application is processed at runtime.  There are a lot of different ways that this can be done, and lots of examples of it in real life.  Over a year ago, I wrote a StackOverflow Answer on this topic.  However, I think it deserves another look.  So let's look at some patterns and common implementations.Communication HandlersThese patterns are designed to handle communication between disjoint ...