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.
WebListManager is a browser based personal "to-do" list web application using Spring and Hibernate. Users can access their to-do lists from anywhere, home or office. A variety of views are provided to see the lists in helpful ways.
The Floranta libraries provide components for building Rich Client Wikis using AJAX or Java. Floranta clients can be embedded in any webpage (even plain html) and allow users to leave notes, images, cards, etc on the pages. Eg: http://www.floranta.com