The shortener, called d0z.me, works as follows: potential attackers visit the site and enter a link they wish to share as well as the URL of a server they wish to attack. When the shortened link is clicked on, users are redirected to the destination, but still more happens:
Finally, yes, to all you a-holes out there, I know, it would be ironic/funny to dos a site that is demonstrating a dos attack. Please don't. I know you can, and that it would be trivial to do, as this server isn't exactly hardened. Let's just save each other the time and hassle and say that you win, theoretical attacker. Congratulations.