8-Bit Dungeon: An Adventure Game of Funny-Shaped Dice

From the introduction:

This is an adventure game, which means that it’s a game which will let the players go on adventures as characters. These characters are pretty varied, and are described below. In a lot of ways, it’s like a video game that a group can play together, and which uses paper, pens, maps, and dice instead of a computer. You have to do the math yourself, but it’s pretty easy math, and it’s easier to change things and add things to the game.