Reddit mentions of Science Fiction Companion (Savage Worlds, S2P10504)

Savage Worlds since this is r/rpg

If it's a fantasy setting, you could just rip Eberron and fit it to your liking.

Edit: saw your other post, since its the far future you could incorporate a Cyberpunk/fantasy setting such as Shadowrun. I'd recommend getting the Fantasy and Sci-Fi companions to give you some ideas and prebuilt objects for the world.

What I enjoy most about Savage Worlds is the amount of flexibility you are given as a GM/Player in that everything has a baseline, and you add flavor to make it something different. Great examples of this are the spells, where it could be a simple "Bolt" spell, but with added flavor such as Fire or Frost, you can change the dynamics of how they work. Plus, the main book you'll need is only 10 dollars.

Just to clarify, there is 1 Core Book (which is, as others have said, all you technically need), and 4 companion books - Super Powers, Science Fiction, Horror, and Fantasy. Then there are numerous setting books such as Deadlands, 50Fathoms (made by Pinnacle), or Beasts & Barbarians (made by the licensee GRAmel).

• Core Book - the stuff you absolutely definitely need
  
• Companion Books - extra optional rules in case you need rules for things like mechas in space (Science Fiction) or sanity rules a la Cthulhu (Horror)
  
• Setting Books - premade worlds for you to play in; often comes with a campaign already made although not always