Integrates Java objects, XML documents, SQL relational databases and LDAP directories in a unified model that allows information to be exchanged, persisted and manipulated in a variety of ways. Supports JDO. [Open Source, BSD-like]
JDO implementation using JDBC. A fork of TJDO with application identity, support for existing schemas, and conformance for J2EE. [Open source, Apache 2 license]
Implementation of Sun's JDO specification (JSR 12), designed to support transparent persistence using any JDBC-compliant database. [Open source, Apache Software License]
Provides interface-based persistence to RDBMSs while allowing developers to focus on the object model, not the physical layer. It implements many of the interfaces specified by JDO. [Open source, GPL]
Jacek Kruszelnicki discusses the issues encountered with persistence, presents traits for an ideal persistence layer, and reviews available JDO solutions.