db4o (database for objects) is the open source object database, native to Java and .NET.
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, 400K footprint.
Ideal for embedded use, e.g., in software running on mobile or medical devices, in packaged software, and for real-time systems.
