Relo - Relationship based Exploration
Relo helps developers explore and understand large codebases. Developers often face code that is hard to understand with over half their time being spent on understanding code. Relo allows developers to easily create relevant and intuitive diagrams, along with features to help automatically build diagrams based on the users past navigation.
While Relo diagrams are similar to UML, they also allow developers to zoom in to view details and edit the code using embedded text editors. These diagrams represent only a small manageable part of the code and do not include irrelevant details, thus allowing a developer to focus on important code relationships.
More detail: http://relo.csail.mit.edu/