Rails Tokeninput 
Rails Tokeninput is a small, lightweight gem which helps to automate installing of the jquery tokeninput plugin, including the standard included stylesheets.
Included Javascripts/Stylesheets
jquery.tokeninput.js
jquery.tokeninput.min.js
token-input-facebook.css
token-input-mac.css
token-input.css
Installation
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.