The Fugue System

Narrative rules for amnesia stories

From the introduction:

The Fugue System is a set of narrative game mechanics usually referred to as RPG rules, designed to let a group of players experience a particular type of interactive game-story.
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Fugue is a mechanical engine that lets you construct and tell the story of a group of people who begin the story with complete amnesia, and who regain their memories of themselves, their pasts, their connections, their abilities and their secrets as the story goes on. What really differentiates it from most RPGs is that it’s built to tell a story that lasts a pre-determined amount of time, and leads to a definite ending.