Free as part of GOG's Winter Sale.
To claim the freebie: Click "Get it here" on the game's page, then "Get for free" in the free giveaway/Oxenfree banner on the GOG homepage.
About Oxenfree: Oxenfree is a supernatural thriller about a group of friends who unwittingly open a ghostly rift. Play as Alex, a bright, rebellious teenager who brings her new stepbrother Jonas to an overnight party on an old military island. The night takes a terrifying turn when you unwittingly open a ghostly gate spawned from the island’s cryptic past.