We Begin at the End
Despite doomsday predictions, the survivors mostly came together. They did the best they could to rebuild pockets of civilization. Electronics and technology were salvaged and rebuilt. Sure, most people still live without power or any post 20th century technology, and almost all the conveniences of 21st century life have been used up, meaning batteries and bullets. But computers are still around, and communications are still possible.
There are cars that still drive, most run on electricity or alternate fuel. Old Gasoline became noncombustible after a few years of sitting around. Steam is a good power source, and solar/electric can be found here and there. Basically modern smart people do the best they can, although there are a few lawless places.
The players have come from wherever and found themselves in Freehaven which is near the coast in southern Oregon. After growing up in this world they are all capable survivors, they have had to be. It is a walled farming community and other than a few cold winter days there are excellent growing conditions and plentiful water. You may have gotten to Freehaven months ago or lived there for a decade (it has only been around that long). Population is around 1500.
Player Characters are built on 100 points and should be skilled capable modern humans. No super powers, no magic, no future tech. Normal tech level is 4 to 5, although knowledge (skills) of tech 7 and 8 is still pretty common and the occasional tech level 9 theories are talked about. Players where all 9 years old when the world fell apart 15 years ago, and have grown into adults in this troubled world.
The real problem are the zombies. Most of the world outside the walls is uninhabitable. There are tales of other 'things' but nobody has first hand knowledge of these dangers. Cities are dangerous beyond imagining. In the lawless lands humans are sometimes more of a threat than zombies. It is rumored that the lands east of the Rockies are ruled by warlords in outlandishly modified cars and trucks.