I hardly remembered it, but after getting the reprint of WEG's Star Wars d6 system, I was reminded that for initiative, players declare their action, and then the skill roll determines initiative.
What other game do something similar? Anybody tried this in a non-d6 system?

Never seen this done in any game. It seems like it would be weird; everybody has prerolled their success (to know what order to do it in), so the round proceeds without any surprises (or does everyone keep their rolls secret until they get to be next in initiative? even so, there's a bound to how successful characters who go later might be) with mostly successes at the start and mostly failures at the end. So no tension like a surprise round to drop the bad guy who will unleash massive destruction, and even the character with the latest initiative might finish them off...

I have seen games where you have to declare actions in advance; in D&D (some editions at least) invisibility ends at the declaration stage if you're going to attack, so enemies see you before you actually attack. It seems like a lot of bookkeeping for modest benefit; maybe for more deliberate characters like spellcasters? But they could act in initiative order but not determine results until later in a round. But I mostly play fantasy RPGs so maybe it works better in science fiction/science fantasy/space opera games. Do Jedi get to know other characters declarations before they make their own?

Not announcing the full results until later in the round can have beneficial effects. Given 4 opponents with 30 HP on average, player characters often focus fire on one to bring it down. If some opponents have 5 HP and some 55 HP, they switch off the weaker opponents once they drop it; varying hit points widely and not revealing whether any target is brought down until the end of the round means that players have an incentive to spread out their attacks, which in turn feels more like what you'd expect.