What would be Ruby on Rails equivalent to PHP Session?
Read here about sessions on RoR.
Basically you need to turn sessions on and off in your controllers. And then access it with something like:
@_session_val = session[:some_val]
Session is a general concept, it's not relative to PHP. Any server-side language has its own implementation to deal with sessions.
First result when googling 'ruby on rails sessions': http://www.quarkruby.com/2007/10/21/sessions-and-cookies-in-ruby-on-rails
Regards