Freeform Creative Play and Sandbox Mode
If a game lets the player use all the facilities that it offers without any restrictions on the amount of time or resources available (other than those imposed by technological limitations), then it supports freeform creative play. Many games that normally offer constrained creative play also include a special mode that removes ordinary constraints. This mode is called the sandbox mode. Sandbox mode lets the player do
whatever he wants but usually doesn't offer the same rewards as the constrained mode—and may not offer any rewards at all. In this mode, the game resembles a tool more than a conventional video game.
The first RollerCoaster Tycoon game did not include a sandbox mode, and reviews of the game cited it as a deficiency. The developers added a sandbox mode to the later editions. Generally speaking, if you are making a game that offers creative play, you should include a sandbox mode if you can. Players enjoy them, and because sandbox modes don't interact much (if at all) with the game's core mechanics, they are fairly easy to tune.
Two particularly interesting, though very early, forms of freeform creative play appeared in Pinball Construction Set and Adventure Construction Set. These games allowed the player to construct games that he or someone else could play. Much of the fun came from trying out the resulting game to see how it played and making refinements—in effect, they permitted game development (within quite restricted domains) without all the work of full-scale development.