adempiere liferay alfresco sugarcrm ...
Sometimes you need a "test bed" for running several simulated scenarios and for that you are NOT interested in writing anything from scratch, rather you require an open source easy to deploy application that can be integrated into your overall system and aid you in your simulation.
There are several options for that, one that I frequently use is to deploy Alfresco (http://www.alfresco.com/) on top of jboss and connect to which ever RDBMS which is under simulation. The advantages are numerous:
1-These are real life working applications whch have been deployed numerous times.
2-They use similar technologies to teh ones you would be probably using (Hiberbane, ehcahe etc)
3-They pose the similar memory footprint and hence can also be used for performance tunning on a VM fro instance.
If you need to setup a system for research and simulation swiftly, I strongly suggest using Alfresco war, jboss/tomcat/jetty and mysql.
The others (adempiere: http://testadempiere.com/webui/, liferay sugarcrm ...) are a bit more involved and would take longer to deploy but they also posses excellent simulation capabilities.