From publisher blurb:
Starfarer’s Codex: Legacy Gunslinger brings the dashing, daring gunslinger concept from the fantasy era into the future! Designed to focus on the most interesting options from the gunslinger class, Legacy Gunslinger allows any character to become an expert in the way of the gun, presenting a Gunslinger feat, a gunslinger archetype (appropriate for any Starfinder Roleplaying Game-compatible class), and special class options for operatives (the gunslinger specialization) and soldiers (the gunslinger fighting style). And, for campaigns where it makes sense for a character to be a gunslinger first and foremost, the 20-level gunslinger base class!
Regardless of how to access them, gunslinger abilities give a character ways to do more with a gun. With abilities drawn from multiple gunslinging methods for any class ranging from 1st level to the top tiers of a campaign, a character can pick up a few gunslinging tricks or become an undisputed master of ranged weapons. So whether you want to gain fancy shooting options that allow you to twirl pistols with the best of them, use gunfire to blast things out of people’s hands, or just want a little extra grit for your character, Starfarer’s Codex: Legacy Gunslinger has got you covered!