Jamon is a text template engine for Java, useful for generating dynamic HTML, XML, or any text-based content. In a typical Model-View-Controller architecture, Jamon clearly is aimed at the View (or presentation) layer.
X4View is a modern framework for developing rich web-based applications in Java. Very easy to use, it doesn't require complex programming model : No JSP/Struts, Servlets, HTML, CSS, XML are needed. See http://www.reasonsphere.com for more details.
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