Grimdark is a roleplaying game that parodies the concept of "grimdark", or the tendency for certain stories to relentlessly emphasize the negative. The basic mechanic involves adding a stat and skill to the sum of a variable number of ten-sided dice, and comparing the total to a target number. From the introduction:

Yes, we thought the world was going to be wonderful millennia ago. Our world used to be full of wonderful dreams, shiny dreams, things we could do. Every human was to be a hero, every home to be a castle, every peasant to be a noble.

And then we got to the stars. That was a terrible idea, because everything out there hates us. This is best exemplified by the grimdark – an all-pervasive field created by the feelings all life shares that their life is the worst of all possible lives, and that their neighbor regardless of station is so much happier. When humanity limited itself to its own system, they only knew their own grimdark, and were unashamed; however, exposure to the grimdark of all the races of the galaxy drove humanity mad.