Alert-me is a simple app that helps me to automate checking the prices for stuff that I like.
There is a rake task that runs daily that visits the page with the product that I want using Capybara/Poltergeist, store the prices in MongoDB document.
If the price is less than the day before it will send an email alerting this. It has a simple dashboard where I display the records from each day in a Sinatra App.