db4o is the open source object database that enables Java and .NET developers to slash development time and costs and achieve unprecedented levels of performance. The unique design of db4o's native object database engine makes it the ideal choice to be embedded in equipment and devices, in packaged software running on mobile or desktop platforms, or in real-time control systems - in short: in all Java and .NET environments, where no database administrator (DBA) is present.
“Using tables to store objects is like driving your car home and then disassembling it to put it in the garage. It can be assembled again in the morning, but one eventually asks whether this is the most efficient way to park a car.”
– Esther Dyson
http://www.db4o.com/about/productinformation/