watchable.rb

module Watchable
  def events
    @events ||= Hash.new { |h,k| h[k] = [] }
  end

  def fire event, *args
    events[event].each { |e| e[*args] }
  end

  def on event, &block
    events[event] << block
  end
end

https://rubygems.org/gems/watchable

You could update the gist and use it as a microgem :)

I absolutely could. ;)