cocoa_alert.rb

#!/usr/bin/env ruby

require 'cocoa'

Cocoa::NSAutoreleasePool.new

app = Cocoa::NSApplication.sharedApplication
app.setActivationPolicy Cocoa::NSApplicationActivationPolicyRegular
app.activateIgnoringOtherApps true

alert = Cocoa::NSAlert.alloc.init.autorelease
i =  ARGV[0]&.to_i  || 3
wait_time = i * 60

sleep wait_time

msg = ARGV[1] || "Tell me what do you want to show, man"

alert.setMessageText msg
alert.runModal