Gephi is an open-source and free visualization and exploration platform for all kinds of networks and complex systems, dynamic and hierarchical graphs. Gephi is available for Windows Linux and Mac OS X.
Gephi is based on an OpenGL rendering engine.
Gephi has just been selected as a Google Summer of Code mentoring organization, and Gephi team is now looking for skilled student applications about a GLSL-based graph visualization engine. More information HERE.