I've found it sometimes difficult to discover certain classes down the hierarchy, and it would be nice to have a way to, for instance, navigate the Exception Class hierarchy.

Preferably some tree widget, showing ancestors, descendants, siblings, etc. Bonus points if there's a way to visualize included modules. Of course since everything is related one way or another, maybe limited to the classes in the same rough "category"?

The problem I'm trying to solve is that I find it difficult to discover the appropriate class unless I already know what class I'm looking for.