Graph Gear is an open platform for graph visualization (the mathematical kind, not the bar chart kind). It allows you to create an interactive graph with force directed layout that has a good interactive user experience.

Graph Gear allows you to quickly render a customizable interaction graph that is described by a graph xml file. All you need to do is embed it in your page and pass the xml over javascript. It provides nice interactive capabilities and a force directed layout.

http://www.creativesynthesis.net/blog/projects/graph-gear/

http://www.creativesynthesis.net/recycling/graphgeardemo/