ESS Model UML Tool
ESS Model is a light weight easy to use Modeling tool that can help you to understand your source as well as other developers source code. It will give you at a glance uml models for classes in the same folder. This shows classes, fields and methods for given classes in a box model. Lines will connect classes in the same package(folder). I use this on my article post here at SDZ some when I feel I have the time. You can make screen shots of the uml using PrtSc on home row then paste into MS Paint, crop, save then insert images in your own post. When you download this put the exe in the path somewhere or add it to the path. Then just navigate to the folder which is the package you want to display. Then type 'essmodel *.java' at the command line.
More about ESS Model
If you right click the image above and view in new pane, then zoom it you can read it just fine.
You can quickly scroll around large diagrams with the overview pane top left by dragging. The dark area is the area in view. If you have classes that are not in packages you can go to default package or all classes to view them. Also there is an unknown package. The lines seem to only indicated parentage such as solid line for extends and dashed for implements.
Copy to Clip Board
You can select a single class image or multi select class images and then select copy to clipboard and then do whatever you want. Such as make small images for articles.
Apparently ESSModel only currently works with Java source or class files and some Delphi files.
Hiding Classes or Files
You can right click and hide some classes from view to remove them from the diagram temporarily. You might want to do this to get a screen shot of only certain classes. Or for selecting only certain classes for copy to clip board with box selection.
Preview and Create Documentation
I didn't care for this feature its not pretty, I'd rather make my docs using javadoc.exe tool and then include these images in the javadocs. But you may like it.
Save to Image File
You can save the whole diagram as an image of type PNG or WMF
Its a good visualization tool
All in all its a very good class UML visualization tool that is light weight and super simple to use. I don't see a way to include multiple packages. So if you are subclassing from different packages within your own project I don't see how it can show those relationships. It only does one package at a time and shows only relationships within that package or with standard Java API classes if they are subclassed or implemented. So below is my rating, Overall its just below 1. Meaning its not weak needs a lot of work to be a great tool but strong enough to be very useful.