This product is usable in any rules system, including the Pathfinder Roleplaying Game and the Swords & Wizardry Roleplaying Game (it is generally "system-less" and focuses on "in-world" information important to player characters.)
A Guide to the Player's Guide
What is this book exactly? This book is not a book of hints, tips, and tricks for playing in Rappan Athuk. Things like, "Be sure to search for the secret door in room 4 on the level of the minotaurs' maze" - you won't find it here. (I don't believe there is such a thing as the above, so don't feel you've gotten something extra there.) This book immerses a player in the world of Rappan Athuk, to let you feel what it's like to live in that world every day. It takes the town of Zelkor's Ferry from being a number on a map and a list of names and game stats to being a place populated with people. The good folks of Zelkor's Ferry have personalities, and the occasional foible, and are available for interaction with your characters. Now when your player characters ride into town, they won't know anybody there, but you will.
Beware - another thing this book is not is a straitjacket. You can't use the things written here to force your GM into (or out of) a particular behavior. "But the book says…" won't hold any weight around here, because we are big believers in Rule 0: "The GM is always right." It may just so happen that in the slightly altered universe in which your characters find themselves, things are a little different than they are in Zelkor's Ferry Prime and they just need to deal with it. In that case, though, it is to be hoped that your GM gives you sufficient information to accommodate his or her changes and feel comfortable in the village nonetheless. (GMs - Hint, hint!)
To be sure, there are specific tips included; grizzled, legless veterans (and some that are merely maimed, not grizzled at all) tell their stories and give their opinions on the crucial things to know about Rappan Athuk and its environs. This information will be useful for folks who have never tackled a dungeon with a population higher than many cities, or those whose alter egos spend so much time in the city or in the great outdoors, that both player and character have forgotten the best way to handle a dungeon. The most important thing to remember about all this advice, though, is that none of it tells everything. Adventurers telling stories of Rappan Athuk are in the same situation as the classic blind men with the elephant: that "each was partly in the right, and all were in the wrong!" We invite you to add your stories to the annals of the Dungeon of Graves!