Graph databases use graph structures (a finite set of ordered pairs or certain entities), with edges, properties and nodes for data storage. It provides index-free adjacency, meaning that every element is directly linked to its neighbour element. No index lookups are necessary. Graph database are faster when it comes to associative data set compared to relational databases. As they do not need join operations, they can scale naturally to large data sets.

Gephi helps people understand and discover graphs and patterns. It uses a 3D engine to show graphs in real-time that can help users make hypothesis, isolate structure singularities or fault during data sourcing. It is written in Java on the Netbeans platform. It can be used to analyse graphs extracted from OrientDB.

FlockDB is a simple graph database and is intended for online low-latency, high throughput environments, like websites. FlockDB is being used by Twitter to store social graphs. It is a distributed graph database and can support complex arithmetic queries. The database is licensed under the Apache License.

GraphBuilder can reveal hidden structures in big data as it can construct graphs out of large sets of data. It is developed by IBM, built in Java, it uses Hadoop and it scales using the Map Reduce parallel processing model. The GraphBuilder library takes care of many of the difficulties of graph construction, such as graph transformation, formation and compression.

InfoGrid is developed in Java and at the heart of it lies the GraphDatabase. It offers many additional software components that makes it easy to develop graph based web applications. InfoGrid is sponsored by NetMesh and they offer also commercial support for using InfoGrid.

InfiniteGraph helps users to ask more complex and deeper questions across their data stores. It can work with massive amounts of distributed data and especially those projects that need more than one server will benefit the most from the graph database. It offers high-speed graph traversals, scalability and parallel consumption of the data.

AllegroGraph is a graph database with MongoDB integration. It is developed for high-speed and high-performance loading and query speed. It uses effective memory utilization and it can scale to massive amounts of quads. It supports SPARQL and RDFS++ and it has a Javascript-based interface.

Gremlin is a graph traversal language and it can be used for graph analysis, query and manipulation. Gremlin works with the graph databases that have included the Blueprints property graph data model. These include among others Neo4j, OrientDB, InfiniteGraph. Gremlin provides native support for Java and Groovy.

HyperGraphDB is a general purpose data storage mechanism designed for knowledge representation. It is based on directed hypergraphs and offers graph-oriented storage. It can be used as an embedded object-oriented database for Java projects or as a NoSQL relational database. The core of the database engine is designed for generalized, typed and directed hypergraphs.

GraphBase is a Graph Database Management System that was built from scratch in order to manage large graphs. It makes huge, very structured data stores possible. Graphbase simplifies the usage of graph-structured data, instead of working with very complex spaghetti-like structures. With GraphBase Singleview, it becomes possible to turn a database into a single, searchable and navigable graph.

Brightstar DB Mobile and Embedded are the open-source tools of BrightstarDB. It is a NoSQL database designed for the .NET platform that is fast, embeddable and scalable. It does not need fixed schema, which gives is a lot of flexibility in what and how the data is stored. Its associative data model fits perfectly with real world applications.

Sparksee (formerly known as DEX), makes space and performance compatible with a small footprint and a fast analysis of large networks. It is natively available for .Net, C++, Python and Java, and covers the whole spectrum of Operating Systems. Sparksee mobile is the first graph database available for iOS and Android.

Neo4j is a graph database boasting massive performance improvements versus relational databases. It is very agile and fast. At the moment it is used by many startups in applications such as social platforms, fraud detection, recommendation engines etc. The data is stored in nodes that are connected by directed, typed relationships with properties of both (a property graph).