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.
Fulworx is a REST framework that uses simple annotations of XWork "Action" implementations to expose restful interfaces. Similar to Struts, Fulworx sits as a controller on top of Restlet. Each action is attached as a resource using Restlets. Standard resources are represented by default as XML (or JSON) using JAXB, but any representation may be specified. Actions may be used in other frameworks such as Struts and Webwork, since they're just XWork implementations.
SerfJ provides a very easy way of developing Java REST Web applications. It helps you to develop your application over an elegant MVC architecture, giving more importance to convention than configuration. This means, for example, you will not need configuration files or annotations in order to specify which view serves a controller's method. However, SerfJ is very flexible, so if you want to jump over those conventions, you can configure the behavior of your applications as you like. The framework tries to meet the JSR 311 specification, but it doesn't follow every point of the specification, because the purpose is to have a very intuitive library, and some some aspects of the specification are out of the scope of SerfJ.
Huxley is a set of classes that makes it trivial to produce legitimate output for queries made by the prevailing standard of REST queries. Instead of writing a network API with many methods, being run over RPC, you instead write only a couple of methods that are accessed by HTTP GET requests. You then return the results (in either XML, JSON, or text) for processing. XML and JSON are chosen because of the ease by which they can be parsed by most languages. In this way, you open up the scope of your network services to many more people than would otherwise have access to it.