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.
Hentai
Due to the vague definitions of any erotic game, depending on its classification, citing the first erotic game is a subjective one. If the definition applies to adult themes, the first game was "Softporn Adventure". Released in America in 1981 for the Apple II, this was a text-based comedic game from On-Line Systems. If eroge is defined as the first graphical depictions and/or Japanese adult themes, it would be Koei's 1982 release of "Night Life". Sexual intercourse is depicted through simple graphic outlines. Notably, "Night Life" was not intended to be erotic so much as an instructional guide "to support married life". A series of "undressing" games appeared as early as 1983, such as "Strip Mahjong". The first anime-styled erotic game was Tenshitachi no Gogo, released in 1985 by JAST. In 1988, ASCII released the first erotic role-playing game, "Chaos Angel". In 1989, AliceSoft released the turn-based RPG "Rance" and ELF released "Dragon Knight".