Put the sun and solar system out to Neptune in orbit around a more massive object, perhaps a black hole. How far from the central object would the sun have to orbit, and how massive must the central object be, in order for the whole arrangement to be stable? Place multiple solar systems in orbit around the central object. How far apart do they need to be spaced for things to be stable? Travel between star systems, each with their own habitable zone, might not be too difficult.
Can such a system naturally form? (Probably not.) Consider astroengineering to construct one.
Stability needs a time scale defined: maybe long enough for life to evolve and set the stage for science fiction.
Inspired by the Firefly system, with multiple stars.