DataNucleus Access Platform 1.0 M2 has just been released with a JDO/JPA API for db4o. Read more here
Main things of interest to db4o users in this release are:
- Added support for db4o "embedded server" mode (contrib from Joe Batt)
- Zip file of Access Platform specifically for db4o, including bundled db4o-6.1 (GPL)
Enjoy! (thanks Andy =)