Java Object Database. It have simple interface like: 'store', 'get', 'delete', and 'query'. BTree algorithm is used for storing and searching. Indexes to allow for fast search. Transactions: 'beginTransactions', 'endTransactions', 'commit', and 'rollback'.

Object database in Java for Java. [Free for non-commercial]

A pure Java object database (ODBMS) component embedded into Java applications to provide object persistence. The j2 OODB is compliant with JDO and is designed for use in embedded systems.

100% pure Java Object Oriented Database, with a simple API and no schema definition language. [Commercial]

Pure object DBMS written entirely in Java. Multi-user with client-server support and garbage collection. [Commercial]

A complex data management and real-time event processing application for Java and C++ applications.

Open source Java Object Database Management System (ODBMS), with multi-user support, object-level access rights, deadlock detection, and XML/DOM support. [Open Source, GPL/LGPL]

Small footprint ODBMS for Java, written in Java. Simple API and customizable query interface. [Free for non-commercial]

An object store implemented in Java. [Open Source, BSD style]

Alpha-quality object-oriented database providing ODMG-conforming Java and C++ language bindings, for Windows and Linux. [Free for personal use]

OODBMS that uses persistent references to scale Java Object Serialization. [Open Source, GPL]