Rails with Active Record and Action Pack
Foundations of Active Record and Action Pack libraries, otherwise known as the basis for the Model View Controller framework that Rails is built on. Which they probably could have said more clearly.
Rails
Ruby on Rails Tutorial (Rails 5)
One of the best examples of context based learning I've seen, this free online textbook teaches Rails concepts by having students build a professional quality web application.
Ruby on Rails: An Introduction
Introduces students to the basics of Ruby on Rails, through an overview of Ruby syntax and a rushed Rails template project.