When it comes to OSR Scifi RPGs, Stars Without Number is the granddaddy of them all, with both a free version and a more expansive paid-for PDF. It's a true OSR sandbox-style RPG.
You can snag the Stars Without Number Revised Starter Collection for a mere 7.95. It includes Stars Without Number Revised Edition, Sixteen Stars and the SWN Revised GM Screen.
The BONUS COLLECTION is approximately 21 bucks and adds in: Starvation Cheap, Suns of Gold, Skyward Steel, Dead Names, and Polychrome.
Damn, but it's a sweet collection. Check your account at Bundle of Holding, as you may have bought this back in 2019.