JustGage is a handy JavaScript plugin for generating and animating nice & clean dashboard gauges. It is based on Raphaƫl library for vector drawing.
Checkout http://justgage.com for details, demos, current release and more.
Usage
In your Gemfile, add:
gem 'justgage-rails'
Require Javascript
Add the following to your application.js:
//= require raphael
//= require justgage
Credits
Rails gem modeled after raphael-rails by Cameron Prebble