The intervening years saw many trends in free-play, the most popular of which was the city-building game. It began in 1982 with Utopia, but the city-building genre really came into its own when it ceased to be strategic/competitive and became instead an exercise in "free" building for its own sake.
The genre grew out of the natural pleasure of designing game-worlds -- a pleasure that game developers experience all the time. One developer, Will Wright, thought that it would be a good idea to share this joy as directly as possible, and this insight led to the development of SimCity, which became a record-breaking success, defining one of the largest genres of the 1990s.
Sometimes this sort of free play was blended with economic simulation, in such as the Tycoon games, starting with Railroad Tycoon (1990). Various more-or-less competition- and objective-oriented games joined its ranks throughout the following decade, from SimIsle to Capitalism (both 1995).
Opening game design to the player, even to a very limited degree, heralded modern player-generated-content games, from Second Life to LittleBigPlanet to Spore.
The metaphor of the "sandbox game" finally emerged at the turn of the century, around the publication The Sims and the following year, Grand Theft Auto III, the two games which are traditionally considered the two original and canonical "sandbox" games.
The invention of the term did indeed accompany a new development in game design, but this was not, as the term suggests, player freedom, which was already available by any number of means: non-linearity; the lack of objectives or central storyline; automatic variation of the game-world and game-behavior.
It was in terms of responsiveness and encouraging player experimentation that these games represented a gradual but transformative change in game design.
"Sandbox" was a new development because it indicated a new promise: automated responsiveness to player behavior. In this sense it does not mean "free play," "non-linear," and the rest; rather, it indicates that which makes this style of play specifically and particularly interesting in its own right.
Most of all, this meant a radical development in design detail. The evolution of sandbox-oriented quality between GTA2 and GTAIII is truly astounding. The switch from bird's eye to 3D opened the world and shifted it from cartoonish "Hot Wheels" platformer to a realistic city. But the critical part was that the writing and detail followed through on the promise.
As mentioned at the beginning, sandbox design facilitates and encourages a sense of player freedom, while providing a framework for play and a rich and detailed world for interaction. This was definitively achieved by The Sims in 2000, and in 2001, Grand Theft Auto III. Let's now consider their innovations, starting with The Sims.
The amazing commercial and cultural success of The Sims might suggest that it was entirely new -- which means we are likely to forget that the genre began with Little Computer People (1985), even though the latter "game" was well celebrated in its time.
This is the birth of the mind game, the virtual seduction.
There were several studies in the 1990s, of what gameplay structures and presentation/interface regimes increase attachment, what exploits the player's tendency and desire to interact in a seemingly meaningful way with the artificial character. These always somehow literalize the metaphor of the game-world, bring the player into the virtual space and enmesh him there: enabling "physical" contact (mouse-petting), sharing "space" (e.g., the player and the character can manipulate the same on-screen objects), and so on.
Today we are so close to such virtuality that it has perhaps become difficult to observe its mechanism, but a primary aspect of sandbox play is the formation of a psychological illusion of contiguity, if not continuity.
Thinking more towards psychologically effective programming, let us consider the dual nature of AI. As any AI designer or programmer will tell you, the task of designing a "believable NPC" involves fostering an appearance or impression of that elusive philosophical notion of intelligence: the psychological impression of intelligence.
What contributes to this impression, however -- the underlying program -- is more or less "intelligent" in an entirely different sense. Where we speak of the "intelligence" of the program, we mean only the level of autonomy and generality. This is not the place to get into the specific maneuvers and techniques, but be assured that relatively simple programming can lead to really convincing NPC AI, and really it's mostly in the presentation.
The NPC programmer's plan, then, is essentially to write suggestive and interpretable behavior, so that the player will "read in" a lot more sophistication than is actually present. Computer-players can be good at winning a chess match or a combat, which has relatively simple rules, easily-validated success cases, etc.
But beyond this, the question of truly intelligent programming (in that ephemeral, philosophical and psychological sense) is well beyond our technological horizon and may well remain there forever. The question of NPC personality in games is always the question of faking it.
The main reason that this trend towards believable characters is compelling for sandbox play is that the characters are, at bottom, more dynamic and interactable. They help "sell" the game world because they seem more realistic. Not "realistic" in the sense that they can ever hope to pass the Turing test, but realistic enough that they'll lull you into forgetting about their artificiality. The more intelligently the NPCs respond, the more the game feels like a free and open world.
AI is widely various and can be complicated, but in general it is effect-oriented. The programmer has in mind a goal behavior, and writes code to meet this objective. In comparison with AI, Artificial Life is bottom-up programming, and it's all about emergence. The emergent behavior is not necessarily even known in advance.
The Sims, and especially the range of games it inspired, was heavily influenced by technological developments in computer science during the 1990s, and in particular Alife. By 2000, this has developed into the art of manipulating automated NPC behavior, even in an otherwise traditional title, as we have for example in Majesty.
In this classic, there is no player-character, and little if any direct action by the player. Instead we have NPC agents whose behavior cannot be directly controlled, but only indirectly influenced in some way: add stimuli and enjoy watching how the automatons respond. It's a delightful gameplay model, which we look forward to revisiting in the forthcoming Majesty sequel.
Playing with automated systems, watching NPC AI agents interact with each other according to their program, or even watching Alife virtual organisms go about their daily life, has long been and remains a key sub-genre of sandbox play. Further, believable and self-motivated characters have become key to sandbox play, because they produce a rich space for interactivity and greatly help establish the open-world aesthetic. But in another style of sandbox games, the game space itself plays this role....