From the RPG Description here on RPGGeek:
Codex is an RPG for writers and other creators who want to use games as a medium to create a world and share stories within it. In Codex, a picture, short story or poem can simultaneously describe a part of the world and a character attribute. Blue, Green and Red books let players develop a cohesive setting for themselves.
A simple yet broad system determines the fates of individuals, groups and even entire nations. The conflict systems cover duels of wit, furious sword fights and massive propaganda campaigns.
Although Codex is designed for your own characters and world, the game includes the city of Eight Gates as an example setting. Use it -- or add it to your own world. You can use Codex as a complete RPG or you can use it to manage the fictional content of other games. It's especially suited to text-based games, including those played by forum or weblog.