The Torus and the Necklace
The Necklace is the thickest part of a gas torus around a neutron star, itself a part of a close binary with a hot F-type star. The neutron star is in orbit 4 - approximately the orbit of Mars in our solar system - and there is nothing inwards of the Neutron star as it has swept up everything. In orbit 7 - about Saturn’s orbit - there is a gas giant with two large moons - Java and Hermes - along with many smaller moons.
The gas torus was formed when a gas giant orbiting the neutron star was slowly stripped off its enormous atmosphere. The gasses stayed in a ring, quickly orbiting the neutron star. The torus changed as life spread into it. Life begets oxygen, and oxygen begets life.
The inspiration for the setting was from Larry Niven’s Integral Trees/The Smoke Ring setting, filtered through an article I found online at http://www.sarna.net/forums/showflat.php/Cat/0/Number/80188/an/0/page/9
The Necklace is the inner, denser part of the gas torus, which is breathable for normal humans and earth animals. There is no hard and fast boundary - the air just gradually gets thinner and thinner. This area is about 20 thousand kilometers in diameter. The area the Altisherpa and their modified animals can live in is about twice the diameter, about 40,000 kilometers across. The entire torus has a thickness diameter of about 2 million kilometers, and an overall diameter of 9 million kilometers.
The Necklace has a volume of 9e15 cubic kilometers. So the mass of the ring is about 0.006 Jovian masses. Very different from a planetary surface; Malthusian limits effectively don't exist. Room for lots of native and alien species without ever managing to encounter them. The torus is full of life adapted to zero G.
The PC Cultures/Species
Pucks: These winged creatures are native to the earth-sized core of the gas giant, now a mostly water world. Their wings are formed like a pterodactyl's - or Smaug's.
Carnivales: These were the first human settlers from earth, arriving after more than a millenium aboard slow boats about 500 years ago. Their ship broke apart while trying to land, and they were spread apart without access to their tech. They live in scattered settlements along the river, with tech levels from stone age to renaissance, and are frequently found in Rasi cities.
Altisherpas: These were the second wave of human settlers, arriving about 400 years ago. They adapted themselves to zero-G life - Altisherpas have hand-feet, are cold tolerant, need far less partial pressure of oxygen in their air, and do not suffer from calcium erosion in zero-G. They live in one great city, and often flake out for a nomad life. Their culture is extremely good at the biological sciences, and do not concentrate too much on physical sciences.
Rasi: These are the last wave of human settlers in The Necklace, arriving 150 years ago. The Rasi live in towns and cities spread along the river from their original settlement. The Rasi make in their own artificial gravity devices, and aggressively graviform free-floating asteroids they wish to colonize.
There are also the Javans and the Hermeans, human cultures who have settled the two large moons of the outer gas giant. Both are frequent visitors to the Necklace, and sometimes stay.
The River is an artifact, constructed with unknown tech by the Builders. It never crosses, or even gets near, the orbit of the planet, instead looping and corkscrewing around that area in the center of the Necklace. It is a gravitational artifact, with the water clinging to the curved line of the gravitational anomaly to a depth of 10 kilometers, making The River 20 kilometers in cylindrical diameter. Rocks - asteroids - have been placed into the river, some entirely submerged, making shallows and reefs, and others protruding above the water. Gravitational pull at the surface is approximately 0.86G, gradually fading into zero G as one gets farther from the source. The slope is steeper than natural gravity, but much more shallow than human-created artificial gravity, which is based on the weak force.
Sometimes relatively slender loops of water only a kilometer or two across arch up out of The River to nearby asteroids and back down. It is possible by these means to visit much of the real estate of the Necklace by boat - if one were immortal. The asteroids these arches lead to have all been graviformed by the Builders long ago. More recently graviformed asteroids - colonized by the Rasi - have no arches leading to them, and the gravity is of the sharply sloping Human type.
There are rafts of vegetation in The River, some of which stretch for kilometers. They are thick enough to grow trees and crops on, and they are sometimes settled, by both Carnivales and Rasi. One cannot built too high on a vegetative mat, or it might prove too heavy for the raft.
The Builders left behind many settlements, cities, and buildings throughout The Necklace. Many have been eroded by time to nothing. Others have been settled in by Carnivales. But some remain largely intact, and unexplored. Who knows what interesting and valuable things were left behind?
The Zero-G Zone
There are plants and animals adapted entirely to life in Zero-G, like the Altisherpas. There are jungle balls, plants growing in no gravity into spherical jungles, each with it’s own ecosystem, with many interconnected plants, animals, and fungi inside. Bubble seas, from meters to tens of kilometers across, replete with fish and plant life, float out there in The Necklace. They can be terribly dangerous if you run into one unprepared. Many flying creatures live in these outlands, though somehow non-flying creatures still end up in jungle balls.
The Outer Limit
This is the area where Altisherpas can live, but other humans can’t. The weather here is cooler, ranging to cold in the outer reaches of the zone. It freezes in winter, when the torus is edge on to the hot sun, and life here is not as lush as in the warmer Necklace. Life still thrives out here. Animals tend to be bigger here, as being larger conserves heat, and their coats are lush and thick.
Winter and Summer
A year on the Necklace is the 32 hours it takes to rotate once around the neutron star, but that is not a usefully differentiated time period. The neutron star revolves around the main star once every 706 standard days, but winter comes twice in that period, as the torus is edge on to the main sun twice in that time, once on each side of the sun. So locals refer to the 353 days between winters as a half year, which is a useful time period. In the inner ring, The Necklace, winter is seen and felt as a dimming of the light and a slight coolness. In the Outer Limit, winter can turn things very cold, as the thin air does not retain heat as well.
The Inner and Outer Stations
There are also 12 huge space stations in the plane of the Necklace - six inside the edge of the torus, and six outside. The inner ones travel faster than the torus, and the outer ones travel slower. They are all large graviformed nickel iron asteroids.