Cayenne is a powerful, full-featured Java Object Relational Mapping framework. It is open source and completely free. One of the main Cayenne distinctions is that it comes with cross-platform modeling GUI tools. This places Cayenne in the league of its own, making it a very attractive choice over both closed source commerical products and traditional ""edit your own XML"" open source solutions.
Platform: Linux, Mac OS, Windows;License: Apache