Hibernate is a popular open source Object-Relational mapping tool. This article by Mario Aquino provides a quick introduction to get started with Hibernate.
A framework that provides transparent persistence of Java objects for JDBC-compliant RDBMS. Implements ODMG 3.0, JDO and uses XML-based O/R Mapping. [Open Source, LGPL]
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 externaliz...
An Object-Relational mapping tool. Generate persistent enable Java source from Class Diagram or ERD. A diagram editor is provided. It can generate code for client applications and server side applications. [Commercial]
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]
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]