Multiselect for Rails 
multi-select is a tiny jQuery plugin to customize selects with the multiple attribute.
The multi-select-rails gem integrates multi-select with the Rails asset pipeline.
Usage
Install multi-select-rails gem
Include multi-select-rails in Gemfile
gem 'multi-select-rails'
Then run bundle install
Include multiselect javascript
Add to your app/assets/javascripts/application.js
//= require multi-select
Include multiselect stylesheet
Add to your app/assets/stylesheets/application.css
*= require multi-select
Updating the gem
There are two rake tasks designed to ease the maintenance of this gem.
The update task pulls the latest multi-select code from github and places images, stylesheets and javascripts in the correct gem paths. It also changes background-image properties in the stylesheet to asset pipeline equivalents.
rake update
The build task is a simple wrapper for gem build
rake build