Part of NodeBox, a Mac OS X application for visualization using Python.
The graph part is described as:
The NodeBox Graph library includes algorithms from NetworkX for betweenness centrality and eigenvector centrality, Connelly Barnes’ implementation of Dijksta shortest paths (here) and the spring layout for JavaScript by Aslak Hellesoy and Dave Hoover (here). The goal of this library is visualization of small graphs (<200 elements), if you need something more robust we recommend using NetworkX.
PS: See my post: NetworkX Introduction… for an introduction to NetworkX.