Hello,
I worked on a new extensible inspector for Pharo (written without OB and so usable directly in Pharo-Core). This tool is based on a tree view of objects in which children can be dynamically extended by simple message overriding. Actions per object menu can be also defined dynamically. A definition panel shows a description of the selected object in the tree. A bottom right pane permits to evaluate some code (in which self is bound to the selected object in the tree).
You can load the code from SqueakSource (NewInspector project). See the class extensions (CompiledMethod, OrderedCollection, Set, Dictionary for the moment) to know how to incorporable your needs.
It is a stable but very young version (I started to code yesterday evening ;)).�Any feedback is welcome :)�
Fr�d