There are currently two implementations of frameworks that implement the spec, allowing a RESTful API to be automatically generated from a domain object model.
Apache Isis is a full-stack open source application development framework, designed to let you rapidly develop domain-driven business enterprise applications, for the Java platform. Its Restful Objects viewer component implements the REST API defined by the spec.
Naked Objects framework runs on the .NET platform, and implements the ‘naked objects pattern’. It was the first framework to fully implement this spec.