"Forty-One" is a darts variant based on the game "301", in which players try to reduce a specific score (in this case 41) down to zero. The special feature of "Forty-One" is that players must both start and finish with a double field.

Here are the basic rules for the dart game "Forty-One":

Objective: The aim of the game is to reach exactly zero points starting from 41.

Gameplay

Double In: To begin the game, players must first hit a double field. This means that a player's first throw must land in a double before they can start scoring points. If a player fails to hit the required double, their score is reset to zero and they must try again to start with a double.

Scoring: After a player has successfully started with a double, they can score points by hitting various sections of the dartboard. The scores are subtracted from 41. For example, if a player scores 20 points in one round, they will have 21 points remaining (41 - 20 = 21).

Double Out: To finish the game, a player must reach exactly zero and hit a double field with their final throw. For example, if a player has 10 points remaining, they must hit the double 5 to win the game.

Busting: If a player scores more points than they have left, their score is reset to zero, and they must again try to hit the required double to start the game.

Winning Conditions: The player who first reaches exactly zero by finishing on a double wins the game.

"Forty-One" is an interesting darts variant that requires skill and precision, especially when it comes to hitting the required double to start and finish the game. As with most darts games, there is room for variations and house rules, but the rules described above provide a solid foundation for playing the game.