An interactive story is a narrative the reader steps into at set points, with what happens next depending on her input. Here every chapter ends with your move: you can say something, do something or wish for something, and the story responds.
The idea predates the phone: gamebooks that sent you to page 47, role-playing at a kitchen table. What's changed is freedom. You don't pick from three buttons; you write what your character says, and the story takes it in.
A good one has memory. The characters remember what passed between you; a no in chapter three still matters in chapter nine. And the story keeps its tone whatever you do. It bends, it doesn't break.
“The Guest in Room 12” shows how it feels. A guest appears at the front desk after midnight and asks questions no one asks a receptionist, and you decide which ones Mara answers. Whether she gets curious or draws a line is up to you, and every answer changes what he asks next.
At Everglow you do not just read it. You are the protagonist, and every chapter ends with your move.