I have had an idea for a sci fi series that's based around "drifter colonies" from my favorite movie, Titan A.E. Though, notably, this universe will have no (known) aliens, and humanity, forced into a mass exodus from a dying earth, take all that they can carry into the stars, welding their aging hulls together into cities that orbit uninhabitable, but stable exoplanets.
The exodus took less than 1% of all humanity from the apocalypse, but all who escaped were in debt to the corporations who undertook the rushed flight from Earth, a debt so large that one's wealth is measured by how low one's inherrited debt is (it suspiciously never goes into the black for anyone but the most loyal of corpo servants). Debt is split (with interest) to all your children, so having 3 or 4 children is common, and colonies are overcrowded.
All wealth is held by corporations, each of which has its own star system(s) and cluster of colony cities. These systems are connected by a Gravity-Pulse-Conveyor network, which uses finely-aimed "grav cannons" that propel your vessel harmlessly through spacetime, the "wave" behind and in front of you being slowed by the machine at the other end. To the passenger, the journey takes months to years. To outsiders, dialation takes effect and generations might pass. The node from Sol to Alpha Centauri has been severed, and no one knows why, but there is a perfect mirror of unknown origin, many lightyears tall and wide right at the midway point between the AC/Sol conveyor. No corporate expidition probes can report back after passing through it.
Most goods are bartered, and the most valuable commodity is culture. Baseballs, silk scarves, CDs, barbie-dolls exchange hands for hydroponic produce, metal scrap, and tools. Corp work can lower your debt and get you paid in work coupons for corporate goods, but that's the minority of transactions.
I'd like it if you'd ask me questions about this world to help me flesh it out. I also welcome ideas!