Does anyone know a good mapping software for an ontological map or a cognitive map for Mac OSX? I'm trying to map all the elements involved in my girlfriend and my relationship and print out a giant poster as a gift for her this Valentine's.

It is going to be a pseudo hierarchical organization of events, people, places and things that have been common to us in the past.

The basic functionality I would need is for it to behave like a directed graph editing software where I can label the edges and nodes. Basic drawing management(spline controlled?) where the edges can be aesthetically placed and arranged. Color coding might be nice but not essential.

The things I've looked at (Freemind/Freeplane and Compendium) either are overkill or are heavily hierarchically based where they won't allow creation of new nodes if it is not a parent/sibling/child of a new node.

So, is there a such a software out there? Anonymous because I want for it to be a surprise.

Thanks a bunch!