Jsgn is a project mainly written in Python, it's free.
Library for JSON Graph notation
A python library around JSGN : JavaScript Graph Notation, an experiment with notations for graphs in JSON.
Example:
{ 'nodes' : { 'node1' : {metadata}, ... } 'edges' : { 'node1' : { 'node2' : {metadata}, 'node3' : ... ... }, ... } }