142-paypal-notifications is a project mainly written in RUBY and JAVASCRIPT, it's free.
Railscasts Episode #142: Paypal Notifications
http://railscasts.com/episodes/142
Commands
script/generate nifty_scaffold payment_notification params:text cart_id:integer status:string transaction_id:string create
rake db:migrate
curl -d "txn_id=3XC103945N720211C&invoice=923204115&payment_status=Completed" http://localhost:3000/payment_notifications