Lines (or Color Lines) is a computer puzzle invented by Oleg Demin and first introduced as a video game in 1992.

Game rules
The game starts with a 9 by 9 board with three balls chosen out of seven different colors. The player can move one ball per turn, and the player may only move a ball to a particular place if there is a path (linked set of vertical and horizontal empty cells) between the current position of the ball and the desired destination. The goal is to remove balls by forming lines (horizontal, vertical or diagonal) of at least five balls (four for beginner) of the same color. If the player does form such lines of at least five (four) balls of the same color, the balls in those lines disappear, and he gains one turn, i.e. he can move another ball. If not, three new balls are added, and the game continues until the board is full.

Game strategy
To achieve the maximum number of points, the player should follow some guidelines:
1. Do not break existing pairs (triples) of balls.
2. Maximize use of existing pairs (triples) of balls.
3. Try to clear the middle of the game field first.
4. Try to keep balls of all colors on the board at all times. Try to avoid situations where a given color is not present on the board to form lines.

Features
In addition to a regular (5 balls per line minimum) game, a beginner setting is available requiring only 4 balls per line. For both skill levels four difficulty variations are available.