title: finding friends in a rails app via facebook, gmail, twitter, etc
body: <p>I have built a social networking app in rails, and am looking for a simple way to allow users to login to their various other accounts (OAuth?) such as facebook, twitter, gmail, other mail clients, etc and see if their friends/contacts on those sites are signed up for my site. </p>
  
  <p>Additionally I will be adding functionality to allow users to invite their non-signed up friends to my site via these same sites.  </p>
  
  <p>In the future I will also want to make it so that users can post their submissions on my site to these various other sites.</p>
  
  <p>At this moment though, the most important feature is enabling users to see which of their contacts on these other sites are signed up for my site.</p>
  
  <p>What is the best way to go about this? What gems should I be looking for (OAuth, RFacebook, Facebooker, etc).</p>
  
  <p>I am currently using restful authentication (Also, can someone point me in the direction of a question that answers how to allow users to sign in, using restful authentication, using their username OR their email?)</p>
  
  <p>Thanks!</p>