Neo4j is an open source graph database. The community and enterprise editions can be used in production without a license (including HA clustering). Licensing is required when you choose not to open source your code that uses Neo4j. When you have a commercial application of Neo4j, the price for the license is well justified so your customers are not impacted when an issue arises in your implementation. Most resolutions are a matter of creating an unmanaged extension that runs code embedded in the JVM.