Neo Technology, sponsoring company of Neo4j, has release the community Edition of Neo4j; making Neo4j available under the GNU General Public License (GPL) and enabling the use of neo4j Community for free wherever you can use MySQL for free. The GPL was basically designed to close the “ASP loophole” in ordinary GPL and enable companies to now be able to provide hosted services based on Neo4j without open-sourcing code modifications or paying for the commercial version. But please seek legal advice regarding open source licenses.