Freeware: Odbms

ObjectDB for Java-JDO 0.97ObjectDB for Java/JDO is a powerful yet compact Object Database ( Odbms ) for Java, written entirely in Java, and compliant with the Java Data Objects (JDO) standard developed by Sun.

db4o 5.5db4o (database for objects) is the open source object database. Features include native Java and .NET object persistence, object-oriented replication, automatic schema recognition, 400K footprint. Ideal for embedded use and in realtime systems.