Skyrails is a social network (or any graph really) visualization system. It has a built in programming language for processing (as far as visualisation attributes goes) the graph and its attributes. The system is not only aimed at expert users though, because through the scripting languages menus can be built and the system can be used by any users.
The main distinguishing point of the system comes from the built in scripting language, the added flexibility of how to represent attributes (nodes can be binded to planes and spheres based on their attributes) and the scriptability of the user interface system. This makes skyrails ideal for creating presentations targeted at the average users.
http://cgi.cse.unsw.edu.au/~wyos/skyrails/
skyrails in action:
http://www.youtube.com/watch?v=I2d312_dXEs