Open worlds and sandbox modes When a level is sufficiently large and open-ended, it may be described as an open world, or "sandbox game", though this term is often used incorrectly. Open-world game designs have existed in some form since the 1980s, such as the space trading game Elite, and often make use of procedurally generated environments. In a game with a sandbox mode, a player may turn off or ignore game objectives, or have unlimited access to items. This can open up possibilities that were not intended by the game designer. A sandbox mode is an option in otherwise goal-oriented games and is distinguished from open-ended games that have no objectives, such as SimCity, and Garry's Mod. Branching storylines Games that employ linear stories are those where the player cannot change the story line or ending of the story. Many video games use a linear structure, thus making them more similar to other fiction. However, it is common for such games to use interactive narration in which a player needs to interact with something before the plot will advance, or nonlinear narratives in which events are portrayed in a non-chronological order. Many games have offered premature endings should the player fail to meet an objective, but these are usually just interruptions in a player's progress rather than actual endings. Even in games with a linear story, players interact with the game world by performing a variety of actions along the way. More recently, some games have begun offering multiple endings to increase the dramatic effect of moral choices within the game, although early examples also exist. Still, some games have gone beyond small choices or special endings, offering a branching storyline (also known as an interactive narrative outside of a video game context), that players may control at critical points in the game. Sometimes the player is given a choice of which branch of the plot to follow, while sometimes the path will be based on the player's success or failure at a specific challenge. For example, Black Isle Studios' Fallout series of role-playing video games features numerous quests where player actions dictate the outcome of the story behind the objectives. Players can eliminate in-game characters permanently from the virtual world should they choose to do so, and by doing so may actually alter the number and type of quests that become available to them as the game progresses.