Caveat: this reply is based on me reading the books several years ago, and will therefore be a bit vague and woolly in places.
The setting is a very far future, transhuman one, with the tech level so high that you can pretty much make anything, anytime, for no ‘cost’ by Star Trek style replicators. Making a city-destroying handgun or a piano made of solid unobtainium is as easy as Captain Picard ordering a cup of tea, earl grey, hot. Unless you are stuck in the middle of nowhere - and even then you may be able to reprogramme your city-destroying handgun into an unobtainium piano maker.
There are a whole bunch of civilisations which have each taken a different transhuman path. (So all the PCs can be from a different civilisation). For instance here are a few:
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The Mechanicians, who have replaced all their organic parts except their brains
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The Eternal Masquerade, who wear programmable masks all their lives. The style of the masks have symbolic meaning, and the wearer alters their personality to fit their chosen mask.
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The Tao of History, a sort of historical re-enactment society dialled up to 11.
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Replicants - they duplicate their minds and bodies, so there can be multiple copies of a person. They also download their memories into newborn babies, in order to ‘reincarnate’.
What do the PCs do? You work for the Patent Office. Powerful AIs get glimpses of the future and send the PCs to ‘crisis points’ where you suppress or promote new ideas/inventions. The aim is to make sure humanity survives into the far, far, far distant future.
SA 1st ed has a mix of dice and diceless mechanics. SA 2nd ed is diceless.
In both there will be things your character can just do, if your skills are high enough. “Yeah I have Cognitech 10 and can calculate wormhole coordinates in my head”.
This is where it gets vague as I can’t quite remember…
Dice version - you rolled 2d10, and multiplied one by you skill score and one by your ‘job’ score, and took the best result, trying to get over a threshold number. It could then get a bit fiddly, because you could spend points from a relevant Theme (romance, intrigue, plot immunity, comprehension, etc) to alter one of the dice rolls. I recall printing out the 13 times table because that was the biggest number you’d multiply by.
Meanwhile, there was a “see a bit of plot in advance” mechanic. This week’s adventure is about the entertainment industry on Tao. But the GM has a row (or several) of index cards on the table, which are the bare bones of future plot, e.g. Because of X, caused by Y, faction A will go to war with faction B. Some of this is revealed by the GM, some the players pay points/take complications to reveal. The players can also pay to alter bits of it, to tailor the future plot to their likes. e.g. it becomes: Because of X, caused by Y, faction A will forge a dynastic marriage with faction B. (This bit intrigued me and was one of the reasons I wanted to run the game).
Diceless version - you give out and accept Complications and Advantages instead of dice rolls. As mentioned, you’ll just be able to do some things, so it will be dealt with narratively. And you have a pool of points to push beyond your normal limits, as well as using Themes, as above.
IIRC there is still a future plot mechanic, but it is created entirely by the players, based on their Themes etc.