Tudu Lists is a J2EE application for managing todo lists. It's based on Spring 2.5, JPA/Hibernate and AJAX (using the DWR framework). It's a simple yet effective project management tool, and it is also often used as a sample Spring application.
JRET (Java Reverse-Engineering Tool) is a program that is capable of reconstructing sequence diagrams from JUnit testsuites through dynamic analysis. It is written in Java/AspectJ and provides a GUI as well as command-line possibilities.