So, I've been working on a setting for a particular RPG for a while now, and just started running it with my group. Figured I'd share it with y'all. I call it "London Rising." It's about giant, city-sized airships in a world mixing magic and steampunk technology. I'm currently running it using the Genesys game system.

Here goes:

London Rising is a dystopian version of earth, where magically-powered airships the size of cities dominate the skies. On the ground below, magical war has rendered most areas of the planet unlivable. It has been almost three thousand years since the outbreak of war drove humanity to live in the sky, and, despite constant maintenance, ships are starting to break down. More frequent landings have been made, even going so far as to stop in dangerous territory. Refueling and refit stops in safe zones take longer. Fear that the great ships will falter and stall is rising. It is impossible to tell if the great era of the air will end soon, or if this is just a hiccup along its path.

Tensions between cities are rising, leading to more than one skirmish between cities. Air piracy has been on the rise, and cities have taken real combat damage for the first time. It's only a matter of time before one falls from the sky.
City ships are separated into three major levels: the officers' quarters, which is nearest to the top decks; the engineers' quarters, which is firmly in the middle, around the flight crystal; and steerage, which is the lower decks. The officers' quarters are where the elite stay, while the engineers' is where the skilled laborers and middle class live. Steerage is for the poor or useless crewmembers, and is cramped and dangerous to live in.

Currency is the cubit, abbreviated as a bit. A cubit is a small brass square with a hole in the middle. Twenty-five cubits can be exchanged for a thruppenny bit, which is a small square of sterling silver with a hole in it. Four thruppenny bits can be exchanged for a dollar, which is a round copper coin with a hole in the middle. The coins are lightly engraved, and are accepted in most civilized places.

Magic is a thing, but must normally be focused through an implement, most commonly a crystal glove.

The two major religions on most city ships are the Temple of the Everlasting Cog and the Order of Skysingers. There is also the Cult of Beth'Shalot, but they are illegal in most places. The Temple is an atheist order that reveres order and solidarity, and despises chaos. They sing hymns called shipsongs five times daily, and worshippers are permitted breaks during these times if they do not work on essential functions. The Order worships the sky and its magic. They have a church on the ship's deck, and all members have free access to it. The Cult worships a sleeping old god who will devour the world when he awakes.
There are mechanical walker machines that are piloted by humans and some that are controlled by rudimentary machine intelligences. These vary in size, but some of the larger ones have built in rocket engines to allow them to fly. Those owned by London are piloted by the Knights of the Silver Cog, a nearly-religious order that is sponsored by the Temple of the Everlasting Cog.

The city is led by Queen Ileein Southmoreland, who handles the city's foreign affairs. The Archchancellor handles day to day affairs and the Captain handles everything about the ship itself.

Day to day affairs are run by Archchancellor Valeria Hightower. The Archchancellor is elected by popular vote, but most of the steerage doesn't really have a chance; the votes are weighted by class. Elections are held every ten years.

The Captain is elected by the Captain's Council, an elite group of ten men and women that run the ship itself. The Captain is a position for life, as when the elected takes the post, they give up their name to bond with the crystal that runs the ship. There is always a captain shadowing the current captain, whose lifespan is drastically reduced due to the taxing nature of their crystalline bond.
The Cogbound are a race of mechanical men created by the Temple of the Everlasting Cog. They are created without inherent sentience, but it can evolve. Those deemed sentient are known as Cogborn, and are revered by the Temple. Every year, all Cogbound take a series of tests called the Sentience Tests, which consist of a large number of empathy-related questions. This happens over the period of a week, which is aptly called Sentience Week. Keeping a Cogbound from their testing is punishable by death in some cases, though whipping and hefty fines are more common.

While mostly human, the populace of London and most other city states has grown varied over the years due to immigration from the surface and a steady stream of emigrants from steerage looking for a better life.

There are three arcane universities in London: St. George's Academy of Sorcery, which is the most elite; Lord Wimbley's School of the Arcane Arts, which is of middling prestige; and the Alderman's House of Spellcraft, which is the state-funded school to make sure all spellcasters have some education.
Most of the world is covered in dark grey wasteland. Only dead plants remain there as far as flora. They are crawling with mutants and monsters, and magical storms are common. Crystals can sometimes be found here, though not very big ones. Mostly big enough for lithospats. Areas of wasteland include much of Europe and Asia, parts of Africa and Russia, and the entire Mediterranean coast.

Magical storms ravage some areas constantly. These places are absolutely filled with monsters and mutants, and what plants do grow there are warped, evil things that grow fat on magical energy. Crystals are abundant here, often being big enough to fly city ships with. Those places include all of north america, most of Russia, and parts of South America.

Most safe zones have isolated themselves, all trade being done via the air. These include India, Japan, Cuba, parts of Scandinavia, Switzerland, the Netherlands, and some areas in the Himalayas and South America's mountain ranges.

Australia is the only country to emerge almost completely unscathed, and is the world's largest trade hub.

Greenland is partially covered in storms, but its safe zones are widely visited trading ports.

Most of the long-lasting technology that exists is ancient crystal-based technology. Newer technology is normally steam-based or more primitive crystal technology, cobbled together by mechanomancers.

City ships are primarily kept aloft by their lift crystals, but are also kept aloft by a variety of other technologies depending on the city, including balloons and steam-powered machines. Propulsion is partially achieved by lift crystals but is mostly provided by steam-powered propellers. Most of the internal systems and living areas are steam-powered, but the officers' quarters are normally crystal-powered.

Smaller airships are normally kept aloft by balloons and steam-powered machines, but some ancient or well-financed airships use smaller lift crystals. Propulsion is almost always provided by propellers.

There are two primary types of small aircraft: gyrospats and lithospats. Gyrospats are little more than a wooden open cockpit, a steam engine, a propeller, and normally some sort of weaponry. Lithospats are separated into ancient and modern lithospats, both powered by lift crystals. Ancient lithospats are elegant, aesthetically pleasing aircraft with no visible means of propulsion. Their crystals are tucked into a protective shell. They are normally made of materials that are now impossible to reproduce with modern technology. Modern lithospats bear more resemblance to gyrospats, but made of steel or iron. Their crystals are normally only protected by a thin hemisphere of metal.

Weapons technology ranges from single shot weapons to clockwork loading mechanisms to weapons firing crystal charges. Melee weapons are fairly standard fare, but also include chainswords and other mechanized weapons.

Advanced locks can either be steam-run transaction engine locks, or crystal-board locks similar to highly tuned modern electronic locks.

Thinking machines are normally run off of crystal-boards, ancient technology that is similar to a modern computer chip or motherboard. The art of making these has been diluted but not lost; with the tools available, it is not possible to make high quality crystal-boards anymore, but the Temple puts out reasonable facsimiles for the Cogbound they make. The quality varies from city to city.