Just like Eclipse, MPS supports views (they are called Tools in MPS). As an example of how to implement editor-synchronized additional tools, we have implemented an outline view. It shows the structure below the currently edited root up to a given level. This level, and the kinds of elements that are shown in this view, is determined by attaching annotations to the language concepts. If a concept has the show in outline annotation, will be shown in the view.
It is really nice to be able to attach any additional data to language definitions using concepts. Instead of coming up with an additional viewpoint model, this often small additional data can just be specified inline as part of the language concept definition itself.