Very simple and powerful list of things that need to be "just done". Created mostly for agile people.
Developed with good desgin (design patterns) using test driven development and clean code principles.
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.