GUESS: The Graph Exploration System by IBM seems a very interesting tool if you have fun managing and playing with graphs but I didn’t have time to try it yet. They say Source code available soon, if you have some desperate need for it in the meantime just email me and GUESS uses some great open source software including Piccolo, JUNG, HSQLDB, Jython , and RServe. I use JUNG and it is a delicious piece of software. If GUESS is able to improuve it and to give something more, it is probably an astonishing piece of software (and it is open source)