[lobster_johnson]

Not entirely true. The only free version is the "Community Edition", which runs on a single node; no clustering support, no monitoring, no hot backups, no caching. [1]

It's pretty much useless in a server environment since even replication isn't possible; if you want a redundant setup -- which you will -- you will have to keep the nodes synchronized yourself. Not to mention that since Neo4j is an in-memory database, it puts a hard limit on your dataset size.

They have a "Personal License" [2], but it lasts for one year and you're not allowed to use it if you have capital funding or a certain amount of revenue.

[1] http://neo4j.com/subscriptions/

[2] http://www.neotechnology.com/terms/personal_us/

[jexp]

Actually much of this is not true. * All Neo4j versions have caching * Neo4j Enterprise is available for free for any AGPL project and for personal use and early startups * Neo4j is not an in-memory database, it is a persistent, fully transactional database, it uses the available memory for caching the hot dataset

[atombender]

> All Neo4j versions have caching

I was actually referring to the "High-Performance Cache" mentioned in the feature matrix.

> Neo4j Enterprise is available for free for any AGPL project

I was really talking about a commercial setting. How many companies deploy a fully open-source project (ie., honouring the requirements of the AGPL) in a redundant data center? Not a lot, I imagine.

> Neo4j is not an in-memory database

True, it seems I was misinformed about that.