The Sandbox Map is an alternative way to play TABS alongside Campaign. In this game mode, there are no point limits, and the player is given the chance to place units on both Red and Blue sides. This lets you test many battles and possibilities (Although there is no changing the limit on Xbox). The player has full access to all units that they have unlocked, and can select from all available maps.
The Sandbox can be used as a makeshift local multiplayer of sorts, where two players can take sides, and the rules can be created to suit the players' needs.
In the Pre-Alpha, the placement map was a grid with no actual way of seeing where the units are going to end up. In Sandbox, you can also choose whatever map you like such as Sahara, Denmark, Japan and Scotland in the Open Alpha. In the Closed Alpha, you have the new Neon map to use. Sandbox is used to create custom battles or to experiment with units. It is probably the most used mode in TABS, because after beating the campaign, it becomes the main feature of TABS.
The Sandbox's interface was slightly edited in the Closed Alpha.
Since there are no monetary restrictions, it is advised that unless you have a very fast computer, avoid placing down too many units. If too many are placed, the frame rate will drop to extremely low rates, and can even crash a low-end CPU that cannot handle much. Landfall also mentioned in the Physics Animation System 2.0 video that the system in the full game will not be as performance heavy as the Alpha's system, so it will allow more units to be placed down in the Sandbox Mode.
Sandbox mode is largely unchanged since the Closed Alpha, although it is still prone to performance issues if a player puts down huge numbers of units, or if they generate a large number of projectiles such as a Cheerleader-boosted Hwacha. Sandbox mode is a great place to look for Secret units, although it is still possible in the campaign as well.
The map Simulation (a totally flat terrain with a grid-like pattern) is exclusive to Sandbox mode.