It's a fantasy space setting which runs highly modified D&D 3.5 rules. It's the latest thought child of Paizo publishing. The core rulebook presents a number of playable races including all the classic alien species archetypes done up nicely. We've got our humans of course, but also bugs, reptiles, green people, four armed people, synthetic people, and rat people. The system has stat blocks for all the classic fantasy races as well, may they never rest.
There are seven classes as well. The Envoy, Mechanic, Mystic, Operative, Solarian, Soldier, and Technomancer. There are 9 themes you build off, Pilot, Bounty Hunter, Icon, Mercenary, Outlaw, Priest, Scholar, Spacefarer, and Xenoseeker. You could also choose to remain themeless. Thus there are 490 combinations, each there own, as race, theme, and class bring there own bonuses to the table.
The rules are all over on the Starfinder SRD.
A key part of the setting is a historic event about 100 years past in which the whole universe seems to have lost all record or recollection of its history over a very long span of time, and at the same time, the human home world vanished. Now that the intergalactic community have recovered somewhat from that, groups loosely aligned by the Pact, are exploring again. There is a loose governmental grip out there in the black.
