RESTEasy is a JBoss project that provides various frameworks to help you build RESTful Web Services and RESTful Java applications. It is a portable implementation of the JAX-RS specification. JAX-RS is a JCP specification that provides a Java API for RESTful Web Services over the HTTP protocol. It is portable to Tomcat and many other app-server. It has rich set of providers for: XML, JSON, YAML, Fastinfoset, Multipart, XOP, Atom, etc.