interface INotifyable
    {
        void Notify();
    }

    class Observed
    {
        List<INotifyable> _mySubscribers = new List<INotifyable>();

        public void DoSomethingCool()
        {
            foreach (var subscriber in _mySubscribers)
            {
                subscriber.Notify();
            }
        }

        public void SubscribeToMe(INotifyable subscriber)
        {
            _mySubscribers.Add(subscriber);
        }
    }

    class Observer1 : INotifyable
    {
        public Observer1(Observed observed)
        {
            observed.SubscribeToMe(this);
        }

        public void Notify()
        {
            Console.WriteLine("ZOMZ: I just saw something cool!");
        }
    }

    class Observer2 : INotifyable
    {
        public Observer2(Observed observed)
        {
            observed.SubscribeToMe(this);
        }

        public void Notify()
        {
            Console.WriteLine("OMFG: I just saw something cool!");
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Observed o = new Observed();
            Observer1 o1 = new Observer1(o);
            Observer2 o2 = new Observer2(o);

            o.DoSomethingCool();

            Console.Read();
        }
    }