...present day [or near future] Earth?
1.
Stick with the ruleset you know best.
2.
Reuse as much as possible or reasonable.
Convert Credits to Dollars (or Euros, or whatever).
This gives you an easy out: Keep the ACTUAL credit listing but call it "Euros". It sounds slightly exotic here in the States, but it's also a real currency, but it allows values to NOT be pegged at the "U.S. dollar" and all of the headache you might get when players might see dollar signs and complain that the prices don't match what they can find on the internet etc etc.
So that handgun that costs Cr300 has become €300. Yay!
(You could use ANY currency... see the last point for clarification)
3.
Limit and explain the essential technology. But,
Map Only As Really Necessary.
- what's the essential TL? 7? 8? 9?
- does gravitics exist?
- how do you get from planet to planet?
- is life support an important matter?
- how is power generated?
- what sensors are available?
- are there robots? clones? synthetics?
4. Map the careers. Again, reuse as much as possible. However, you may want to redefine and adjust "Navy" for instance.
- army, marines: no change
- entertainers: no change
- scholars: no change
- citizens: no change
- agent: no change
- rogue: no change
- noble: no change
- scouts: needs a name change
- navy: needs a description change
- merchants: might not exist
- psioncist might not exist -- PSIONICS might not exist!
5. Create a
skills blacklist. Only worry about skills that
absolutely "cannot" exist. Let the rest live as-is. Keep It Simple. It should be a short and obvious list.
- Fleet Tactics
- Grav craft ?
- Astrogator
- Gravitics ?
- Turret Gunner ?
- Jump Drive tech
- Battle Dress
- Spines ?
- Psionicology ? (depends if you want psionics)
6. Map the vehicles and equipment.
know what equipment captures the feel of the setting.
- are there gauss guns? lasers? plasma? particle accelerators? meson guns?
7.
Know what captures the feel of the setting.
- Outland
- Alien?
- Blade Runner
- 2001: A Space Odyssey
- Space: 1999
- The Expanse?
- Jack McDevitt's novels (set around 2200 AD, a bit further than "near" future).
If the political structure of the world is slightly different from today, then you'll need a
Map Of The Earth and you'll have to make decisions.
Make any decisions that you like. Do
NOT be bound by analysis or other peoples' opinions. This is a game.
One side effect: you'll probably want to use the dominant country's currency sign for the prices of things. So instead of Cr300, you'd have
€300. (Euros). <-- I like this one best.
元300. (Yuan)
L300. (Lira). <-- My second choice.
₺300. (Turkish Lira)
₹300. (Rupees)
₽300. (Rubles)
...or whatever. Just avoid emoji or else your players will be distracted.
I like the straightforward "L", for Lira or Libre or whatever, but it begs the question: where did this currency arise from? Did Greece suddenly stumble upon such overwhelming material, technical, and political power that it now dominates the world? Or is this the currency of the North American Union? Or something else entirely??
If you can deal with those points, then you have a viable setting for adventures.