999: The Novel is based on the 2010 DS game also known as Zero Escape, focusing on the game's narrative by removing DS version's puzzles and instead offering players a choose-you-own-adventure story experience. The iOS app first launched in Japan last summer.
999: The Novel from writer Kotaro Uchikoshi promises to take readers on "a suspense-filled journey full of danger, terrifying choices and unexpected twists toward a variety of endings that may or may not see them coming out alive on the other side." A direct sequel, Zero Escape: Virtue's Last Reward, launched on DS and Vita in North America in late 2012.
999: 9 Hours, 9 Persons, 9 Doors (iOS)