Hibernate Developer Wizard
The new Hibernate Tools contain a wizard for reverse engineering a database schema and for automatic generation POJO files and cfg.xml Hibernate files - exciting stuff! For now, this is an Eclipse plugin, and I have not been using Eclipse much lately (sort of addicted to IntelliJ). It would be great if eventually these tools were also wrapped as custom ant tasks (and/or command line tools). [Update: reader Max pointed out that the tools do have ant wrappers - the latest version that I downloaded was packaged as Eclipse plugins but a tools jar that is included is independent of Eclipse - my mistake.]
Hibernate supports more interesting (complex) data relationships than Ruby on Rails, but both tools taken together cover a lot of application development space.