I won't say too much about "One" because the secret is the game. One, a.k.a. "The Angstloch," was introduced in 2018 at DefCon 26. Several dozen copies of the game were put into play. A few other copies of the game were handed out to friends who couldn't make it to Vegas that year.
The game includes a puzzle which remains unsolved.
I may re-release it at some point in the future, if there's ever any interest.