You might UMLGraph useful. It leverages GraphViz/dot as do most such graphing tools. I haven't used it, so I can't give a review of it, however.
That being said, you might also be able to roll your own minimalistic diagramming tool just using GraphViz and dot.
I've used GraphViz/dot to generate many useful types of diagrams, from visualizations of Spring contexts to IntelliJ module dependencies, to visualizations of complex XML documents. Look around and see what you find.
