This is just a really great Fate setting. Part 'kitchen sink', part 'Afterlife simulator', the stories of Oubliette rely on a different definition of the 'struggle for survival'.
Death isn't a thing in Oubliette. Run away from a debt owed, and your debtors have eternity to find you. Not even death is an escape, as you can be murdered and the truly despicable can haunt your "respawn point" or trap you so long in bondage that your place of bondage becomes your new respawn point. So many games are 'game over' when you die. Not so in Oubliette. You will return. More traumatized, perhaps, but there is no escape from the continued omnipresence of existence....decades, centuries, millennia, eras of existence.
Unsurprisingly, the vast majority of the population of Oubliette is unable to handle the mental strain of eternity. These are known as the Broken, and they fill the streets, even laying in vast piles after throwing themselves into the blackness, seeking nothing more than catatonia to escape.
You are one of the Unbroken. Some goal, some relationship, something about you makes you a bit more resilient to the Breaking than others. You're most likely destined to Break at some point, and if you're lucky, return to the Unbroken.
You might change forms over the course of centuries, eventually ascending (or descending) to a form completely different than the one you entered the World of the Forgotten. You may rise (or fall) in power level (called Caste).
There's no limit to who or what you might encounter, befriend, or oppose. It's a world of endless possibility. A dark fantasy sandbox that has a unique, vibrant setting that makes you want to explore it.
Around every corner there could be anything. Literally! Literally anything. A god. A dragon. A vampire. Tiny chittering eyeless goblins. A collapsing tower filled with sentient plant monsters.
It's probably one of the best illustrators of the power and flexibility of the Fate system, too, and the book is just chock full of hooks, races, factions, npcs, adventure ideas....honestly, you'll get your money's worth with this book. It's not just a pamphlet with a couple ideas. It's a rich sourcebook that is like a bomb of creativity that should be able to fund a nearly-infinite number of adventures.
You could go through an entire campaign and merely move a character from one caste to a higher caste as they ascend in power level. In most games, this is the end of your story. In Oubliette? There's always something bigger, and now you'll have enemies and challenges scaled to your new power level, as you begin to control and direct a bit more of the world.
The book is well-organized, and full of beautiful and evocative art. The lore is incredibly interesting (I didn't find anything I wanted to skip because it was 'boring'), and it leads naturally into character creation some 4 chapters into the book. The latter chapters are for the GM. But there's a wealth of information here for players and GMs alike.
A special note about the Bestiary section, which deserves special mention. A lot is made of the Fate of Freeport book, but the Bestiary section of that book is tiny compared to the massive, massive number of NPCs detailed in this book.
The Bestiary spans from pages 239 - 368. That is over a hundred pages and literally hundreds of interesting characters and beasts and monsters roaming the streets and open spaces, the cracks, the bowels, and the gleaming towers of Oubliette, of all different power levels from Refuse to Divine, and everything in between.
It's a world I want to live in, and explore, for many years to come. (Although, perhaps not for eternity. I'll leave that to the real denizens of the World of the Forgotten.)