Open Graph is a protocol that is used to integrate any web page into the social graph.
RackCache is a quick drop-in component to enable HTTP caching for Rack-based applications.
reCAPTCHA is a free service from Google that helps protect websites from spam and abuse.
Ruby on Rails is a server-side web application framework written in Ruby under the MIT License.
Twitter is a 'microblogging' system that allows you to send and receive short posts called tweets.