The Neo4j community edition is now free and licensed under GPL (http://neo4j.org/download/ http://neo4j.org/download/), and they are working on an Enterprise li

The Neo4j community edition is now free and licensed under GPL (http://neo4j.org/download/ http://neo4j.org/download/), and they are working on an Enterprise license that is free for startups (https://groups.google.com/d/msg/gremlin-users/kw9N6xYb6l4/uHW23ukWsukJ https://groups.google.com/d/msg/gremlin-users/kw9N6xYb6l4/uH...). There is also a Neo4j Heroku Add On (http://addons.heroku.com/neo4j http://addons.heroku.com/neo4j) that is currently free for developers.