Grid Runner is a top-down game similar to tag. The object of the game is to change a set amount of flags scattered around the playfield to the colour of your player. Upon starting the game, two players must race to find the first flag. The first player to get to this flag will change the flag's color to blue or red (player 1 or player 2's color, respectively). The loser will then be marked as "it" and must then hunt down the other player "tagging" them and making them "it" instead. Only the player not marked as "it" may change the colours of the flags, and as soon as the desired number of flags have been changed, that player will win.
The map takes a grid-like form, featuring numerous types of tiles allowing the player to speed up in one direction, teleport or allow further pathways to appear. Each player is armed with a laser gun that can slow the opponent down, and each player may build "bridges" to overcome gaps. You may also use magic found on the map to slow down your opponent, teleport or speed up. Shields and time for the bonus stages are also collectible.
Each level is split into three rounds against an opponent, which the player must win in order to succeed. Opponents often come with handicaps, giving them better control on ice for example, or being able to build two "bridges" at once. After each level there is a bonus level in which more magic can be obtained.
Source: Wikipedia, "Grid Runner", available under the CC-BY-SA License.