A thin wrapper around https://github.com/msurguy/ladda-bootstrap.
Gemfile:
gem 'ladda-bootstrap-rails', :git => 'git://github.com/vendji/ladda-bootstrap-rails.git'
application.js:
//= require spin
//= require ladda
application.css:
*= require ladda-themeless