Bookkeeper is a Rails engine with the aim of allowing a Rails application (at least 3.1) to handle the purchases you made and their receipt.
Configure
Add to your Gemfile
gem 'bookkeeper'
then launch bundle install.
Mount the engine wherever you prefer. To do so, add to config/routes.rb:
mount Bookkeeper::Engine => "/bookkeeper"
or, if you prefer:
mount Bookkeeper::Engine => "/"
root to: 'bookkeeper::purchases#index'
Bookkeeper uses Twitter Bootstrap markup, if your app doesn't use Bootstrap or you want to overwrite Bookkeeper views, just create the view into app/views/bookkeeper/. Use gem's views as template.