We’re using the Fate Core game system with a few adjustments and adaptations. Compared to many other game systems, Fate is much more oriented toward story and narrative than mechanical complexity. A free online version of Fate can be found at here. You can pay what you like for a PDF of Fate Core or purchase a printed copy here. To play the game, it would be helpful to at least read over chapter 1 (The Basics).
Note that these rule adaptations have not been play tested. If anything turns out to not work, cause serious unbalance issues, or just not be fun, we’ll change it. If we need new rules, then those will be added.