This is a clone of db4o (database for objects).
It was developed, commercially licensed and supported by Versant.
db4o is written in Java and .NET and provides the respective APIs. db4o can run on any operating system that supports Java or .NET. db4o is offered under multiple licenses, including the GNU General Public License (GPL), the db4o Opensource Compatibility License (dOCL), and a commercial license for use in proprietary software.
Actian, the owner of Versant, stopped development on db4o and made it available at their currently defunct website: http://http://www.db4o.com:
With regret we have to announce that Actian decided not to actively pursue and promote the commercial db4o product offering for new customers any longer.
Since the db4o dual licensing model allows for the free usage of the community edition of db4o for non-commercial purposes, you have the opportunity to continue to use it for your non-commercial applications or even fork it to provide support for the community.
For a limited time, you can find the subversion repository under https://source.db4o.com/db4o (currently inaccessible) and the latest installer packages including the source tarball for Java, .NET35, .NET40