yEd is a very powerful graph editor that can be used to quickly and effectively
generate drawings and to apply automatic layouts to a range of different
diagrams and networks.
yEd makes full use of the yFiles library. This is a Java class library enabling
the viewing, editing, optimizing, drawing, and animating of a wide range
of diagrams, networks, and other graph-like structures.

WWW: http://www.yworks.com/en/products_yed_about.html