[JoshTriplett]

neo4j uses the GPL (specifically version 3), not the Affero GPL. You can build a service based on the community edition without sharing the source of your service; you only need to distribute source (under a GPLv3-compatible license) if you distribute your service to others.

(Summary of the Affero GPL: you must distribute the full source of your service, under an AGPL-compatible FOSS license, to the users of your service. Summary of the GPL: you must distribute the full source of your program, under a GPL-compatible license, to anyone you distribute your program to.)

It does look like the "Community" edition leaves out the clustering features, so if you need those you'd likely need a license for the proprietary version.