Resteasy is a JBoss.org project aimed at providing productivity frameworks for developing client and server RESTful applications and services in Java. It is mainly a JAX-RS implementation but you'll find some other experimental code in the repository.
JAX-RS
------
The JAX-RS code is in the jaxrs directory. After pulling down a clone of the Resteasy repository, cd to jaxrs/ and just do mvn install to build.