From the back of the book:
Humans have been in space tens of thousands of years, and societies have risen and fallen so many times that no one remembers where we come from.
Colonies are grouped in clusters of a few systems connected by slipstreams – artifacts of the cosmos or perhaps a forgotten technology. Only the slipstreams allow travel faster than light. Apart from that, spacecraft make do with reaction drives, dumping heat as best they can.
Diaspora is a self-contained role-playing game, with rules for starship battles, individual combat, social interaction, and platoon-scale engagement, in an original science fiction setting that you help design.
This is your universe. How are you going to survive?