Open Source NoSQL Databases in Java

Apache Cassandra is a distributed wide-column database for high availability and linear scalability. It offers a Dynamo-style partitioner and Bigtable-like column families with tunable consistency.

Apache HBase is a distributed, versioned column store modeled after Bigtable, built on Hadoop HDFS. It supports MapReduce integration, server-side filters, Thrift and REST gateways, and real-time read/write access.

HyperGraphDB is an embeddable, open-source graph database for generalized hypergraphs. It provides an extensible type system, graph traversal, Java object storage, transactions, and optional P2P distribution; built on Berkeley DB.

Neo4j is a graph database for storing and querying data as nodes, relationships, and properties. It provides a native storage engine, Cypher query language, ACID transactions, and can be deployed as a server or embedded. The community edition is open source (GPL v3).

OrientDB is a multi-model NoSQL database combining graph and document models. It supports SQL, ACID transactions, distributed deployment, and schema-less or schema-full storage with physical links between records.

Berkeley DB Java Edition is an embedded, transactional key-value store in Java with ACID support, replication, and a Java Collections-style API. It runs in-process with no client/server overhead and is maintained by Oracle.

Perst is an object-oriented embedded database for Java and . NET with ACID transactions and concurrent access. It offers B-tree, R-tree, and other index types with a small footprint and transparent persistence.

Terrastore is a distributed document store built on Terracotta clustering, with HTTP access, JSON documents, partitioning, and map/reduce. Development ceased around 2011; code is preserved on GitHub and Google Code Archive.

Voldemort is a distributed key-value store (Dynamo-style) with automatic replication and partitioning, pluggable serialization, and no single point of failure. Originally developed by LinkedIn; source remains on GitHub.

MyOODB is an object-oriented database and web environment with distributed objects, nested transactions, and web tunneling; part of the MyOOSDK with MyOOWEB for small, fast applications.

NeoDatis ODB is an object-oriented database and transparent persistence layer for Java, . NET, Groovy, Scala, and Android. It persists native objects directly and can run embedded or in client/server mode.