The latest version of Ruby on Rails has a new framework and API mode.
Rails 5.0 is being described by the developers as:
"without a doubt the best, most complete version of Rails yet."
The two headline improvements are a new framework for handling WebSockets, and support for API mode.
Action Cable provides access to your entire Active Record and PORO domain model in your WebSockets work. The developers have added a new ActionController::Renderer system that you can use to render your templates outside of controllers, so you can reuse server-side templates for WebSocket responses.
In development, Action Cable runs in-process with the rest of your app. Doing this has meant the default development server has been switched from Webrick to Puma. The developers say that in production, you may well want to run Action Cable servers in their own processes, whcih is how it is used at Basecamp at scale.