Creating Plugin – custom page class (module?)

If you look at xdforum plugin, it is accessed with a ?a=xdforum

I am interested in creating a mysql table and defining an object that users could contribute

say fruitlist.php

so fruitlist would manage its own objects. Much like xdforum. I don’t understand how this fits in to the whole hook / action classification of plugins

ex ?a=fruitlist <– default display
?a=fruitlist&action=add_new
?a=fruitlist&action=modify&fruit_id=23

… etc etc

I want to integrate my own classes and objects with wordpress but am unsure where the seam is that xdforum is using….

I feel like this has to be a common desire amongst people, but i’m not sure what exactly its called. Perhaps someone could link a plugin doing something similar to this that isnt as beastly as xdforum

Thanks