289-paypal-recurring-billing is a project mainly written in RUBY and COFFEESCRIPT, it's free.
RailsCasts Episode #289: PayPal Recurring Billing
http://railscasts.com/episodes/289-paypal-recurring-billing
Commands used in episode
rails g migration add_paypal_to_subscriptions paypal_customer_token:string paypal_recurring_profile_token:string rake db:migrate