10,000 years ago humanity broke away from a ruined Earth and started building space stations in the orbital path of Earth. They mined Earth for most of it's natural resources, and captured asteroids for more. Earth is a shell of what it once was, with a single lone city supported by a vast forest, solar arrays, and geothermal engines. They cling to the past, and have built a mythology around the essence of being human.
Other humans had escaped to Mars. The harsh environment, and long slow process of on-going terraforming has left them with a surprising little grasp of life. They will do anything to survive and are generally a hard resourceful group of people. It is clear the frontiersmen spirit is alive and well with them. Although the embracing of the smaller gravity has left them weakened and dependent on their tools.
Not much is heard from the those that went to Europa. They still live deep under the frozen crust in the warm water. They found life, they exist symbiotically with it. That is all that's known outside their insular civilization. Sometimes telescopes pick up surface activity. What is known about these people are that the low gravity and high pressure have produced humans that resemble sleek marine animals and are odd to the normal eye.
The builders of the space stations named them after their Zodiac house they were in when Earth was abandoned en masse. Once a year, Alignment Day is celebrated. However, over time the space stations started squabbling amongst themselves and broke off into factions. Slowly people migrated until clear delineations began to form. Speciation had occurred and via accretion those space stations became vast swarms of infrastructure.
By far the most successful society are the Companies. Huge enterprises that are fundamental to the survival and existence of all the stations. They are contracted by all, and serve their very powerful masters. They have built up huge shipping lanes, travel lanes, and communication relays. Of the society dependent on them, they adhere to corporate law and are severely honorific. The corporations spend lots of money on their employees, and loyalty exists amongst whole tribes of relatives. These companies battle each other while still sharing services. Embrace, extinguish.
Of course, not all humans rely on the corporations. When humans figured out how to nueral map themselves into computers some of them went rogue. They launched their supercomputers for near-immortality only to spend large amounts of time gathering resources from space debris and protecting themselves. Some of them still adopt the quaint image of being space pirates. While the essence of their humanity is disputed, they still launch many exploratory missions. With the extra time granted to them they start to seek answers. For humanity has suffered consequences through this expansion.
Two major events occurred in this network of satellites. Some humans went after the smooth exterior and luxurious refinement that only nanotech can provide. While the humans lived incredible long lifespans, and could do stupendous things, they were very dependent on their tech. A software virus, or maybe bug, ripped through their culture and left deformed monsters mocking their once beauty. They have no control over the tech anymore, and even though every once in a while one of them appears that can communicate with the outside world, little is known about their descent to barbarism.
The second event was a shock to all of recorded history. The Europa surprise was a gift of intricate life. Yet it was nowhere near our intellect. From undetected origins, intelligent lifeforms crashed into our ecosystem. They started taking over stations like mold by spreading and consuming. Hideously foreign creatures roam space and dare any intrepid adventurer to face them. Some refugees claim they have a taste for blood, and some claim that they themselves have a war going on. Nobody has been able to hail them. And yet, they survive.