Pathfinder: Shadow of Chernobyl
"Have you ever thought about how Sidorovich and the Barkeep both know how much each Pathfinder is owed, what they're due to bring back or what supplies they've asked for? I ain't ever seen messengers running between them.
What I've heard is that they've each got a book, a magical one, and whatever is written on one also appears on the other. Makes sense, don't you think?"