Restlet is a REST framework for Java. It supports all REST concepts (Resource, Representation, Connector, Component, etc.) and is suitable for both client and server Web applications. It supports major Web standards like HTTP, SMTP, XML, JSON, WADL, and Atom. Many extensions are also available to integrate with Servlet, Spring, Jetty, Grizzly, Simple, JAXB, JAX-RS, JiBX, Velocity, or FreeMarker. A GWT version is also available.
JWAA is a software framework for building dynamic Web applications as networks of first-class Java objects. XML is used for representing information normally coded as HTML. The XML files are automatically reloaded when they change. It has a "persistent forms" feature in which form data automatically persists in the database such that fields behave like pieces of paper that automatically preserve what's written on them. This default behavior is easily overridden. Invalid links are reported at XML load time via the browser, and are also recorded in log files.
Simple is a truly embeddable open source application server and Web framework. It has consistently out-performed both commercial and open source Java Servlet engines and has a fully comprehensive API that is as usable for experienced Java developers as it is for beginners. It also contains a lightweight Struts Tiles-like framework for presentation, which can be used with either Velocity or Groovy templates.
HttpdBase4J is an embeddable Java Web server framework that supports HTTP, HTTPS, templated content, and serving content from inside an archive or from the classpath. The classes are easy to extend as they utilize the "don't call us, we'll call you" principle to allow the user to override the framework behavior during all the different phases of the HTTP transaction.
WebComp is a tool for using scripting to compose and configure Web sites from various existing components, such as static HTML, Java Servlets, Java server pages, and others. It includes a scripting language, a component model/framework, and a set of basic pluggable components to use with it. It is based on Java Servlets.
Dwarf HTTP Server is a full-featured Web server with a Java Servlet API 2.2 implementation and JSP support. Since it is based on the Dwarf framework, it shares its common design principles: powerful security architecture, modularity and extensibility, XML-based configuration, uniform logging, and remote management.