There isn't a lot of competition in the "free/libre database" market though. The only serious players are Jena/Fuseki (an RDF store) and Janus (a graph store).

There is also Cayley (https://github.com/cayleygraph/cayley) which supports more query languages, including GraphQL, and multiple backend stores.

Cayley is cool! A 20% project from Google iirc

But it's not a "native" store. It's just a layer on top of other RDBMSes.

There's also https://github.com/postgraphql/postgraphql

PostgraphQL generates a GraphQL API from a PostgreSQL database. It won't change how your data is modeled or queried at the database level, i.e., it is NOT a graph database project like Agens, Neo4j, Cayley, etc.

This isn't a graph database, it's GraphQL which is an (unfortunately named) interface or "language" to query data, regardless of what the underlying database or data model is.

I can vouch for this one. I've been building apps with PostGraphQL for about a year and love it. The dev community around that project is strong.

I've been watching https://dgraph.io with great interest. Looks like it could become a very solid contender as a horizontally scalable open source graph database engine.

Dgraph seems to be the most promising along with http://janusgraph.org/ for scalable graphs.

Oh? Neo4j is free. The Community edition is GPLv3, and the Enterprise edition is AGPLv3.

The Enterprise Edition is not AGPL. It's under one of "Neo4j Commercial License", "Neo4j Evaluation License", "Neo4j Educational License", or "Fair Trade Licensing". In other words it's not free. Why would I want to use the "Community Edition" of a company whose interest is to force me into buying their Enterprise Edition? The more people use this "Community Edition", and the more they are encouraged to force their "Enterprise Edition" under my throat, because "it will be easier to buy a proprietary plugin than change database". They are already restricting the use of important features such as "Unlimited graph size", "Database storage reallocation", "Schema constraints", "Runtime to accelerate common queries", "Role-based security", "Kerberos Security", "Load balancing", etc. Why would I want to get into this?! I'd rather spend my time learning and contributing to Jena or Janus than a bait "Community Edition".

The "enterprise edition" is AGPL. Feel free to interpret it differently then Neo does, but the license is AGPL [1]. Anyways, I don't understand the hostility. They're tying to walk the line between a profitable company selling software while still doing it all in the open. The fact that they kept things open source and not closed was one of the things I loved about working there.

1. https://github.com/neo4j/neo4j/blob/3.3/README.asciidoc

So, are you saying that Neo4j is 100% free as in "100% AGPL, otherwise Commercial License if you don't want to use the AGPL"? In other words, the code is exactly the same, only with a different license?

Yes, that is the case.

According to [this page](https://neo4j.com/editions/) it's not. In fact, they are restricting important functionalities to their Enterprise Edition exclusively. Which means, the codebase is not the same.

Yes, the Community Edition and the Enterprise Edition are different. Certain functionality is restricted to the Enterprise Edition. It's a different codebase. I didn't say otherwise.

You can see it here: http://github.com/neo4j/neo4j

See how there are 'community' and 'enterprise' top-level directories? The 'enterprise' directory contains the enterprise-specific code. It's a separate project in some senses but it does share the same repository, and it is open source.

As you can also see by looking at that repository, the Enterprise Edition is licensed as AGPL. Here is the license: https://github.com/neo4j/neo4j/blob/3.3/enterprise/LICENSE.t...

I'll quote:

    If you have not executed a Commercial Agreement with Neo Technology, the
    Software is subject to the terms of the GNU AFFERO 
    GENERAL PUBLIC LICENSE
    Version 3, as follows:

Then follows the AGPL license.

It is AGPL; it's dual licensed. You can use it freely under the terms of AGPL, or you can enter into a commercial agreement with Neo Technology and use it without the restrictions imposed by the AGPL.

Here's the license: https://github.com/neo4j/neo4j/blob/3.3/enterprise/LICENSE.t...

There's nothing wrong with companies charging for software products.

I agree. This is not the point though, nor what I said.

It reminded me http://grakn.ai , another quite solid and interesting project right know.

Well some of the competitions regardless of free or commerical are built using either a known NoSQL or a known relational database as the backend.