Elements like ActionView and other rendering modules have been removed because they are for developers who do not deal with front-ends, little relevance. Important functions for back-ends such as creating REST endpoints, the data in JSON format and save them to adopt Rails-compliant manner are also top on Rails API. In the README file of the project Twitters API is cited as an example of an application that manages JSON requests so.
The project has been running for several months, but the developers have only now decided to make their framework publicized. The source code is licensed under the MIT license and it is available on Github.