The one who pulls out the sword will be crowned king is a short experimental game about pulling a sword from a stone to be crowned king, like in the Arthurian legend. You grab the sword with your mouse and try to pull it out from the stone. If you are able to get it all the way out, you will prove that you are the rightful king and as such you will be crowned.
However, you are not the only one trying. Each time someone else online pulls it out, the sword will get longer and heavier. The more you wait, the harder it will be. If you manage to pull it out, you will receive a corresponding achievement proving that you are a king and not a peasant.