"Bootstrap is a toolkit from Twitter designed to kickstart development of webapps and sites. It includes base CSS and HTML for typography, forms, buttons, tables, grids, navigation, and more.

twitter-bootstrap-rails project integrates Bootstrap CSS toolkit for Rails Asset Pipeline (Rails 4, 3.1, 3.2 are supported)"

More MVC stuff and you have to like Bootstrap. There is a reference to Railscasts, which can help to get you up and running.