http://www.yworks.com/en/products_yed_about.html
That’s pretty much all you need to know. yED lets you stick polygons graphically into blank space, label them, and draw connections between them haphazardly, then click a single menu to automatically reorganize the jumble you made in any order you like – hierarchical, tree, organic, circle, UML, etc. It also supports import of existing data. Cross-platform, open-source, awesome.
