Trey Causey has done some amazing work in the RPG field over the years, and Strange Stars is probably one of his highest regarded releases. Even if you don't run it as is, due to being system neutral and chock full of ideas, you could literally mine this for ideas in your own sci-fi RPG campaign for years.
Until tomorrow morning, Strange Stars is on sale in PDF(marked down from 9.99) to 4 bucks.
It's the far future, Old Earth is lost and shrouded in legend, and the children of paleo-humanity have long ago populated the stars, branching into new forms and strange cultures. Adventure is measured in light-years!
Strange Stars is a setting for any game where modern transhuman science fiction meets classic 70s space opera. Join a salvage mission to steal ancient tech from the wreck of a deranged sophont warship. Become a skiptracer in the lawless orbital megapolis of Interzone. Plan an elaborate data-vault heist on a diamond planet. Cross ceramic blades with a Zao Pirate in hard vacuum. Score sweet dreams or nightmare fuel from the oneirochemists of Eidolon. It's all somewhere in the Strange Stars!