COBRA
An object persistence layer written in Java which uses a relational database to provide persistent storage, whilst shielding programmers from the details of relational database access. [Open Source, GPL]

DB Objects for Java
Lightweight and flexible solution for storing and retrieving java objects into and from relational databases, without using SQL. [Open Source, LGPL]

Osage
Object-Relational mapping for JDBC databases, with XML features. [Open Source, LGPL]

CocoBase Enterprise O/R
Object/Relational mapping tool, with customized mappings for each major EJB server (including JBoss). [Commercial]

jRelationalFramework
A lightweight framework that was written to automate the most tedious 80% of relational database access coding and leave the other 20% to the developer. [Open Source, MPL]

DODS (Data Object Design Studio)
An Object-Relational Mapping Framework with a GUI Editor that lets you automatically create Java objects that map to relational databases. [Open Source, Mozilla-like]

ObJectBridge
A framework that provides transparent persistence of Java objects for JDBC-compliant RDBMS. Provides an ODMG 3.0 compatible transactional object server as a client-interface and uses XML-based O/R Mapping. [Open Source, LGPL]

jStorm
Simple tool for object-relational mapping, based on DbObjects, with mechanisms for aggregation and concurrency stamps. [Open Source, GPL]

Object-Relational Mapping
Information and facts about object-relational mapping products, architecture problem-solving, and direction in product comparison and selection.

SerializeDB
A library for mapping Java objects to a relational database. [Free developer and commercial enterprise editions]

Abra
A Java library and a set of tools that can be used for storing and retrieving Java objects in a relational database. [Open source, BSD license]

SimpleORM - Simple Object Relational Mapper
Implement low overhead object/relational mapping on top of Java JDBC. [Open source]

Prevayler - Transparent Persistence for Java
Write plain Java classes: no pre or post-processing required; runs on any VM; no inheritance from base-class required. [Open source, LGPL]

J-Database Exchange (JDX)
A cross-platform solution for transactional persistence of Java objects . By Software Tree, Inc. [Commercial]

JDO vs. EJB by Gopalan Suresh Raj
Compares and contrasts the Two Persistence Frameworks provided Java. Java Data Objects(JDO) which provides Language Transparent Orthogonal Persistence with Enterprise JavaBeans(EJB) that provides Functional Persistence.

Apache OJB
An Object/Relational mapping tool that allows transparent persistence for Java objects against relational databases. Provides JDO and ODMG APIs. [Open Source, Apache]

JORM (Java Object Repository Mapping)
The ObjectWeb open source adaptable persistence service. It is used to offer CMP 2.0 for the JOnAS server, as well as Speedo, a JDO implementation. [Open source, LGPL]

Torque
An XML-based persistence layer. Part of the Apache Jakarta family. [Open Source, BSD-like]

CarrierWave
Provides the following features: build generated client side data objects structurally mirroring server side business objects; pluggable persistence; pluggable binding between client and server; pluggable query mechanism; zero-configuration externalization and internalization of server state into and from XML. [Open source, GPL]

Player (Persistence Layer)
For relational databases. [Open source]

JDBM
A simple transactional persistence engine for Java. It can used to store a mix of objects and BLOBs, and all updates are done in a transactionally safe manner. JDBM also provides scalable data structures, such as HTree and B+Tree, to support persistence of large object collections. [Open source, BSD License]

FireStorm
Generates persistence tier and query service for relational databases. Generated code is based on the Data Access Object (DAO) design pattern. It offers the choice of generating implementation logic based on JDBC or EJB. [Commercial]

TopLink
Object-relational bridge by Oracle. Available for Java, WebLogic, and WebSphere. [Commercial]

FormPers
A persistence framework with forms automation. It support on-the-fly SQL table creation/structure modification base on definition in Java class, automated form creation and automated form result parsing. [Freeware]

XML Persistence
An Java transactional XML DOM persistence (PDOM) library. Using W3C DOM Java API, developers can store partial or complete document in database. [Open source, BSD License]

Hibernate
An object/relational persistence and query service for Java. To support a rapid build procedure, Hibernate rejects the use of code generation or bytecode processing. Instead runtime reflection is used and SQL generation occurs at system startup time. [Open source, LGPL]

sysXs
A platform for integration and automation for the use in enterprises. It provide XML based persistent object services for Web server Java servlets and Java applications. [Commercial]

iBatis
XML-based Object/Relational mapping and persistence framework as well as a data access abstraction layer. [Open source]

Object Matter
Provides an Object/Relational mapping tool with a persistence layer. Also features an introduction to Object/Relational mapping. [Commercial]

Jaxor
Simple and lightweight Object/Relational mapping and persistence framework. Configuration is stored in XML files and code generation relies on Apache velocity templates. [Open Source, Apache]