db4o Open Source Object Database
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 mobile devices, in packaged software or in real-time control systems.
db4o is available here for free download. The download includes an interactive version of the odbms tutorial for JAVA (PDF) or .NET (PDF)to get started quickly.