Recaptcha-rails3-noplugin-example is a project mainly written in ..., it's free.
A sample rails 3 app that implementes reCAPTCHA without any plugins
This is a sample project which shows how to use reCAPTHA with a rails 3 project. refer http://thekindofme.wordpress.com/2010/09/25/recaptcha-with-rails-3-without-plugins/