IPMessage.net is a concept which allows you to send a message to any Ip address. The message itself doesnt go to that ip address but when the person with that IP visits the same site he sees the message displayed for him.
The idea is simple and pretty unique as it not only tells your IP but also allows you to send message which you can use it for private or secret message. I am not sure if this is going to work if somebody is using proxy.
So if you want to secretly send somebody a message and you know his or her Ip this can come in handy. Try IP Message
Related : Chat on Lan with IP Messenger