SubEthaSMTP is an easy to understand Java library that provides a receptive SMTP server component. By plugging this component into your Java application, you can easily receive SMTP mail using a simple abstract Java interface. Also included is a small sub-project called Wiser, an easy to use incoming mail testing framework.
GreenMail is a suite of email servers for testing purposes and sandbox development. It supports SMTP, POP3, and IMAP (including SSL) and can be embedded into any Java application or unit test. The GreenMail Service (SAR) extension runs as a JBoss embedded developer mail server sandbox, manageable via JMX.
OpenEJB is a simple, lightweight Enterprise JavaBeans (EJB) container and server. You can embed OpenEJB in your own applications, or in a Web application server like Tomcat, or run it as a standalone EJB server. It supports EJB 3.0, 2.1, 2.0, and 1.1, and has partial support for EJB 3.1.
Architecture Rules is a Java library that allows a programmer to assert code's architecture via unit tests or ant tasks. This test is able to assert that specific packages do not depend on others and is able to check for and report on cyclic dependencies among your project's packages and classes. This project wraps a industry accepted JDepend to simplify the process of maintaining a solid software architecture.
The Spiffy Framework is a collection of well-tested and often used helper methods and utility classes. Such methods and classes solve existing and recurring practical problems, and remedy annoying features of the Java language or its frameworks. The value of this framework is not only the code, but also the ideas for solutions to the problems. The goals are to collect and centralize "utility abstractions", and to serve as a repository of knowledge/smart ideas for programmers to learn.
AppFuse is an application for "kickstarting" Web application development. It allows you to execute a single ant task to create a skeleton application based on Struts, Spring, and Hibernate running on Tomcat and MySQL. It uses Ant, XDoclet, Spring, Hibernate (or iBATIS), JUnit, jMock, StrutsTestCase, Canoo's WebTest, Struts Menu, Display Tag Library, OSCache, JSTL, and Struts. (Spring MVC, WebWork, Tapestry and JSF are also options.)