I didn’t get very far in it but I’d have to say Ironseed, a DOS space trading/combat game in the vein of Elite: Dangerous or Star Control 2 which is a much harder sci-fi take than usual on the concept. Crucially, it has no FTL travel. This has several ramifications:

• Your crew members don’t have organic bodies; they’re effectively chemical suspensions of brain matter linked directly into the ship’s control system.
• Traveling over the vast interstellar distances slowly drives your crew insane. You have to have the ship’s psychiatrist treat them to counter this (or, in desperate cases, restore their minds from backup - but this also causes them to lose any skill points accrued since the backup was made).
• There is no universal ingame currency because no civilization lasts for the thousands of years it takes to journey between stars. You have to barter for everything.
• Planets can undergo significant geological changes. You might visit your favorite trade hub only to find out that a volcanic eruption wiped out the global civilization sometime in the past few centuries.

The soundtrack is also dope as hell.