Based on the 17th-century pistol dueling game for iPhone "Pistols at Dawn" by Cedar Hill Games and Tobyn Manthorpe.
Players take turns playing cards to move their crosshairs to stay on target or to move the opponent's crosshairs off target. There are three types of targeting cards that move a player's crosshairs, their opponent's crosshairs, or both. Players can earn "shot points" which can be used to purchase special abilities from the shop.
Play alternates between players until both players pass. A player will only pass if they cannot play a card or purchase abilities. After both players have passed, any crosshairs in the red zone score a hit on their opponent.
Keep your opponent off-target while you take aim and fire.
Regarding the iOS app that this game is inspired by, "Pistols at Dawn, a great game that no one played." Tobyn Manthorpe
-description from designer