The proof-of-concept application I use whenever I test any development framework. It is trivial yet the domain model contains embedded objects, one-to-one, one-to-many and many-to-many relationships. So it lets me flex most framework features. In this version, it is a Maven based Groovy project using Hibernate JPA. Groovy 1.7.0 Hibernate 3.5.1-Final I'll slap a web front end on it when I get a chance.