Rails Tokeninput is a small, lightweight gem which helps to automate installing of the jquery tokeninput plugin, including the standard included stylesheets.

jquery.tokeninput.js
jquery.tokeninput.min.js

token-input-facebook.css
token-input-mac.css
token-input.css

This gem should work out of the box. All you have to do is add the gem to your Gemfile:

gem 'rails_tokeninput'

Then bundle install or update (depending on if you want to upgrade an older version of this gem).

bundle install
bundle update

In your assets/javascripts/application.js, you will need to add d3 to your manifest:

//= require jquery
.
.
//= require jquery.tokeninput

In your assets/stylesheets/application.css, you can add the stylesheets you want by including them in your css manifest:

*= require_self
.
.
*= require token-input-facebook
..etc.