prepend_view_path is your friend when you want to use different views in the same app for different configurations, e.g. same code for different apps/sites/etc:

class ApplicationController ....
   prepend_view_path Rails.root.join('app', 'views', ENV['APP'])
end

prepend_view_path can also be called e.g. once per request before rendering the view to have different view templates for each subdomain, user, cat, etc.