» Ozone    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]    http://ozone-db.org/

» CudenDB    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    http://www.geocities.com/cudendb/

» FastObjects j2    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.    http://www.versant.com/en_US/products/fastobjects

» JYD Object Database    Pure object DBMS written entirely in Java. Multi-user with client-server support and garbage collection. [Commercial]    http://www.jyd.com/

» Jeevan    100% pure Java Object Oriented Database, with a simple API and no schema definition language. [Commercial]    http://www.w3apps.com/index.jsp

» MyOODB ( My Object-Oriented Database & Web Services )    A database and Web Services (SDK), includes documentation, example code and information about the author.    http://www.myoodb.org/

» ObjectDB    A full featured Object Database for Java, written entirely in Java. JDO compliant. [Free for non-commercial]    http://www.objectdb.com/

» ObjectStore    A complex data management and real-time event processing application for Java and C++ applications.    http://www.progress.com/objectstore/index.ssp

» SOD    Alpha-quality object-oriented database providing ODMG-conforming Java and C++ language bindings, for Windows and Linux. [Free for personal use]    http://www.tneumann.de/sod/index.html

» Sieben Geisslein    An object store implemented in Java. [Open Source, BSD style]    http://siebeng.sourceforge.net/

» db4o    Object database in Java for Java. [Free for non-commercial]    http://www.db4o.com/