Spelljammer Kingdom Hearts
This is a world built upon the foundations of war. One could say that the technology on this one got started pretty nicely during their Victorian Era, kind of progressing a steampunk feel. With time, that technology continues to advance into more of a dieselpunk setup. The first World War unleashes weapons of mass destruction. The world is told that the weapons are nuclear. Most of the world is made uninhabitable, and most people become refugees, migrating into a space that is perhaps 25% of what they used to occupy, creating vast, hyper-densely populated metropolises. In North America, the MegaCity is on the east coast, stretching from what used to be Boston all the way down to what was Atlanta. Communication is much less common outside the City walls. The government's primary focus is on the other megacities out there, and because of that, there's a lot of crime running rampant on the inside. What they didn't know before they all shrunk down to a quarter of the space, was that humans were not alone. They brought their shadows with them. Vampires adapted to the new situation, running the criminal underworld. Werewolves, on the other hand, have stayed out in the Wastes, to run free in the wilderness, their natural tenacity keeping them alive.
The most common form of transportation for the rich is air travel: dirigibles. Lighter than air craft are the way to fly, for the most part, complete with some particularly large and armored dirigibles having runways on the top of their balloons for the small aircraft they use as their weapons: biplanes. New advances in dirigible technology allow them to rise to the edge of the atmosphere, where they can go over the contaminated Wastes between the Megacities. Inside the Megacities, public transportation in the form of horizontal and vertical rails are the most common way to get around. It started originally as a subterranean rail system, a subway system. As construction grew more and more vertical, as the population grew and the real estate stayed the same, what was once served adequately by elevators and stairways was not enough. So they created another tram system to connect the rails, a vertical tram system.
Something else is also afoot. While vampires, werewolves, even some mages have been here for centuries, perhaps even millennia, there are other things leaking through the edges of reality now, brought by the tides of Shadow that the Hellmouths opened this universe to.
Most of the playing in this universe will take place on a local level in Precinct 2342. This precinct is home to several hundred thousand people. It’s a small city on its own, surrounded by many more just like it. Like all but the highest precincts, this one is mostly a ghetto of slums. There are many different factors at play that most of the people in this world know nothing about.