Open world
There is no consensus on what the earliest open world game is, due to differing definitions of how large or open a world needs to be. Ars Technica traces the concept back to the free-roaming exploration of 1976 text adventure game "Colossal Cave Adventure", which inspired the free-roaming exploration of "Adventure" (1980), but notes that it wasn't until 1984 that what "we now know as open-world gaming" took on a "definite shape" with 1984 space simulator "Elite", considered a pioneer of the open world; Gamasutra argues that its open-ended sandbox style is rooted in flight simulators, such as SubLOGIC's "Flight Simulator" (1979/1980), noting most flight sims "offer a 'free flight' mode that allows players to simply pilot the aircraft and explore the virtual world". Others trace the concept back to 1981 CRPG "", which had a free-roaming overworld map inspired by tabletop RPG "Dungeons & Dragons". The overworld maps of the first five "Ultima" games, released up to 1988, lacked a single, unified scale, with towns and other places represented as icons; this style was adopted by the first three "Dragon Quest" games, released from 1986 to 1988 in Japan.
Gamebook
"The Adventures of You" series, authored by Edward Packard and R.A. Montgomery and initially published by Vermont Crossroads Press, laid much of the groundwork for the later surge in popularity of the gamebook format. The series was born with "Sugarcane Island" by Edward Packard, which was written in 1969 but did not see publication until 1976. The series later included "Journey Under the Sea" by R. A. Montgomery (1977). After the series' end, two standalone gamebooks authored by Packard would follow, both published by Lippincott: "Deadwood City" (1978) and "The Third Planet from Altair" (1979). While these early efforts apparently achieved some popularity with readers, they (and the gamebook format in general) still did not have a publisher with the marketing strength required to make them available to mass audiences.
Packard and Montgomery took the idea of publishing interactive books to Bantam, and thus the Choose Your Own Adventure (CYOA) series was born in 1979, beginning with "The Cave of Time". The series became immensely popular worldwide and several titles were translated into more than 25 languages. The series reached the peak of its popularity with children in the eighties. It was during this period that Bantam released several other interactive series to capitalize on the popularity of the medium (a few examples are: Choose your Own Adventure for Younger Readers, Time Machine and Be An Interplanetary Spy). Many other American publishers released their own series to compete with CYOA. One of the most popular competitors seems to have been TSR, who released several branching-path novels based on their own role-playing games. The most famous TSR series was Endless Quest. Another strong competitor was Ballantine with their Find Your Fate series, which featured adventures in the Indiana Jones, James Bond and Doctor Who universes. Famous author R. L. Stine wrote several books for this line, including "The Badlands of Hark", as well as for other series such as Wizards, Warriors and You. Several Choose your Own Adventure spin-offs and many competing series were translated into other languages.