Db4o for Java

db4o (database for objects) is the open source object database, native to Java. Free software, available under the GPL and under a commercial license. Persist any object with one line of code. Other features are object-oriented replication, Native Queries, automatic schema recognition, 350K footprint. Ideal for embedded use, e.g., in software running on mobile or medical devices, in packaged software, and for real-time systems.