Ammentos is a lightweight persistence framework for JDK 5. It does not require any installation nor configuration; just put a jar file into your classpath and start writing code. It is designed so that your persistence code will be dramatically short and so that you won't have to spend a lot of time to learn how to use it. It is about 72Kb large and it does not require any external library except for your database JDBC driver. You can use it in desktop applications or in server-based environments.
Apache Cayenne is a persistence framework that provides object-relational mapping (ORM) and remoting services. It has a wealth of unique and powerful features and can address a wide range of persistence needs. Cayenne seamlessly binds one or more database schemas directly to Java objects, managing atomic commit and rollbacks, SQL generation, joins, sequences, and more. With Cayenne's Remote Object Persistence, those Java objects can even be persisted out to clients via Web Services. With native XML serialization, objects can be even further persisted to non-Java clients.
Apache Geronimo is an easy-to-use implementation of the Java 2 Platform, Enterprise Edition (J2EE). As a full application server, Geronimo provides support for Java Servlet and JavaServer Pages through either Tomcat or Jetty, JMS through ActiveMQ, EJB through OpenEJB, Java Persistence API through OpenJPA, ESB through ServiceMix, and more. It is also combined with enterprise grade configuration and management. Geronimo 1.1.1 has passed the J2EE certification test suite and it is officially J2EE certified.