The Hadoop Distributed File System (HDFS) is the primary data storage system used by Hadoop applications. It employs a NameNode and DataNode architecture to implement a distributed file system that provides high-performance access to data across highly scalable Hadoop clusters.

Amazon Neptune is a fast, reliable, fully managed graph database service that makes it easy to build and run applications that work with highly connected datasets. The core of Amazon Neptune is a purpose-built, high-performance graph database engine optimized for storing billions of relationships and querying the graph with milliseconds latency. Amazon Neptune supports popular graph models Property Graph and W3C's RDF, and their respective query languages Apache TinkerPop Gremlin and SPARQL, allowing you to easily build queries that efficiently navigate highly connected datasets.

Neo4j is a graph database management system developed by Neo4j, Inc. Described by its developers as an ACID-compliant transactional database with native graph storage and processing, Neo4j is the most popular graph database according to DB-Engines ranking, and the 22nd most popular database overall. 

More info https://neo4j.com/

“A complete, distributed, parallel graph computing platform supporting web-scale data analytics in real-time”

MapR Database is a high-performance NoSQL (“Not Only SQL”) database management system built into the MapR Data Platform. It is a highly scalable multi-model database that brings together operations and analytics as well as real-time streaming and database workloads to enable a broader set of next-generation data-intensive applications in organizations.

See https://mapr.com/products/mapr-database/

• Webinar - GraphDB Fundamentals Adding Meaning to Your Data
• GraphDB Website and Documentation
• GraphDB Fu