> Let me clear. I want to permit the use of a method to only inherited
> classes but not by other classes. This method should be, something like
> protected.

Protected exists in Ruby. Just call 'protected'

class Foo
  def this_method_is_public; end;

  protected

  def this_method_is_protected; end;

  private

  def this_method_is_private; end
end