Sodbox, the Simple Object Database for XML, is a fork of the Perst database. Actually, it's not a real "fork", but just a place to experiment with some ideas. If you are interested in a Java object-oriented database, I'd recommend you check out Perst instead of Sodbox.
Perst was originally written by Konstantin Knizhnik. McObject continues development on Perst today and, like Knizhnik, releases it under a GPL license.
Questions about Sodbox can be directed to Kevin S. Clarke ksclarke@ksclarke.io