DataNucleus AccessPlatform provides persistence of Java objects to RDBMS, LDAP, XML, db4o, NeoDatis, Excel and JSON datastores. We have just released version 1.0.3, and 1.1 Milestone 3.
Version 1.0.3 is for use with JDK1.3+, and adds support for native queries with LDAP, Xcalia/Kodo style datastore-identity, and makes Enhancer API improvements, as well as fixing some bugs with large result sets and replication.
Version 1.1 M3 is for use with JDK1.5+, and adds support for JDO2.3 Enhancer API, native queries with LDAP, JPA2 @OrderColumn, auto-start using metadata files, persistence of interface/Object fields to a single column with RDBMS (for compatibility with Xcalia/Kodo-generated RDBMS schemas), JDO2PersistenceManager proxy, as well as fixing some bugs with large result sets and replication. This version also includes much refactoring for supporting other RDBMS-like datastores, and preparation for the forthcoming JDO2.3 Metadata API.
You can read more about DataNucleus AccessPlatform here.