Latchworks: The Keyholders
Latchworks is an alternate reality game about the Society of Keyholders, who keep what others lose. It is told through nine puzzle books (The Keyholders, standalone Field Dispatches that chain into a hidden meta, and small Pocket Primers) whose ciphers hand off to each other until the last one opens the door, every lock generated and proven solvable before a page is printed.
latch.works is the other half: a society desk with fragments hidden under a magnifier, a board of a dozen Signals left in the world (a personals ad, a lost letter, a spectrogram of static, a page only the robots are meant to find), a keyhole that takes every word you recover, and a portal that tracks your rank from Applicant to Archivist.