Django REST framework is a lightweight REST framework for Django that aims to make it easy to build well-connected, self-describing RESTful Web APIs. It creates self-documenting Web APIs that include a Django admin style frontend. It has a modular, flexible architecture using Django's class based views. API creation can be as simple as adding a couple of lines to urls.py.
Guzzle is a RESTful Web service client framework that enables PHP developers to quickly build testable Web service clients utilizing HTTP/1.1 best practices. It gives you access to advanced features like persistent HTTP connections, parallel requests, exponential backoff, over the wire logging, MD5 validation, cookie jars, and a caching forward proxy.
RestyGWT is a GWT generator for REST services and JSON encoded data transfer objects. RestyGWT Rest Services allow you to define an asynchronous service API which is then implemented via GWT deferred binding by RestyGWT. It features generation of asynchronous RESTful JSON based service proxies, encoding and decoding of Java objects to JSON, and an easy-to-use REST API.
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.
VRaptor3 is a fully-fledged Java Web framework focused on fast development and maintainable code. It intends to make RESTful application development easy. A resource corresponds to a business logic annotated with its path and HTTP method. It runs inside DI Containers (Spring or Pico out of the box) and, therefore, enables full integration with them. Also, using Hibernate is easier: its session is automatically injected by VRaptor, so you just have to use it. VRaptor3 is refactor-friendly, especially in its redirecting configuration. It is also nicely extensible.
WebMotion is a Web application development framework based on a REST architecture and the Java EE 6 standard. It features a presentation layer management using pages (JSP, HTML, etc.) and REST service exposition (e.g. XHR calls). It enables you to serialize service results into JSON or XML. The framework has deliberately limited capabilities, but it focuses on the ease of use. It leaves open the choice of persistence framework, dependency injection, and validation.
XINS is a technology used to define, create, and invoke remote APIs. XINS is specification-oriented. When API specifications are written (in XML), XINS will transform them to HTML-based documentation and Java code for both the client-side and the server-side. The communication is based on HTTP. XINS competes with the complex SOAP technology. Main design goals include simplicity, scalability, and testability. XINS is not only a specification technology, but also an application development framework. It offers transaction logging, unique log documentation, and active code generation.