I'm finishing up an Apocalypse World game and planning on starting another. My current game took sort of a Mad Max vibe for the setting--wide open wasteland, with a few pockets of urban maze left.
This time I want to set the game in a heavily urban area, inspired by Hamsterdam from teevee series 'The Wire', Kowloon Walled City in China, and the quarantine zone in the movie 'Blindness'. My idea is that when civilization began to crumble and the maelstrom began to form, the governments of the world started to put the poor (the untouchables) into what amounted to fortified concentration camps, which themselves were just walled off and secured sections of big cities. Automatic security systems were set up, and the world forgot about the people inside.
These places were called "Harm Reduction" zones, and were unpatroled, unprotected, and unknown to the general populace.
Then the end came, and the security systems that were supposed to keep the untouchables in ended up keeping the screaming hordes of mutants, pissed-off raiders, and physical manifestations of pure hatred out.
When things calmed down, the untouchables were all that was left. They turned the security measures of the camps to their benefit, and scavenge out in the areas beyond the safety of the walls. There were sometimes two or three of these zones in larger cities, and now they trade or war against each other.
There were dozens of these zones set up in various cities all over the world, and the game would focus on one that people simply call 'Sanctuary'. It's set in one of the cities that had a few of these zones, to make for interesting interactions.