gistfile1.rb

module Extensions
  extend ActiveSupport::Concern

  included do
    @@after_end_callbacks = []
  end

  module ClassMethods
    def after_end(*callbacks)
      @@after_end_callbacks = callbacks
    end
  end
end

class Model < ActiveRecord::Base
  include Extensions

  after_end :foo, :bar

  def after_end_callbacks
    @@after_end_callbacks
  end
end

puts Model.new.after_end_callbacks # []