Surgeon Simulator 2013 is an odd duck. What began as a simple browser-based game seemingly gained popularity overnight, to the point where even Valve became involved with the title when its developers decided to run an ARG (Alternate Reality Game) tied to the title.
Provided you know the answers to the ARG, you will gain access to what may be the most amazing surgery performed: alien transplants. There's not one, but six of them for you to work on.
Here's a video showing the entire process:
