Fireboy and Watergirl

Fireboy and Watergirl is a cooperative puzzle platformer for two players sharing one keyboard - one controls the fire boy, the other the water girl, and together they must make their way through a temple full of traps, where fire must never touch water, water must never touch fire, and neither of them may touch the poisonous green slime. Every level therefore requires the players to coordinate jumps, levers and platforms in the right order, because what one character can safely cross often kills the other. The players must constantly think ahead about which of the pair goes first and who has to wait, so the path works for both of them at once.

This emphasis on cooperation between two people at one computer was unusual among Flash games in 2009 - most titles aimed at solo play, while Fireboy and Watergirl bet on a shared experience, ideal for family or friends playing together. The graphics are simple, with the two characters clearly distinguished by color against a dark temple setting that legibly signals dangerous surfaces - lava, water and toxic sludge alike. This visual simplicity actually serves the game well, since the player has to instantly recognize which character is allowed to cross where.

The series was created by studio Oslo Albet, and thanks to the success of the first installment it was followed by a string of sequels with new temples and puzzles, making Fireboy and Watergirl one of the longest-running browser game franchises. It's still played today mainly for its simple but effective cooperative mechanic, which needs no explanation or tutorial - just a willingness to communicate with the other player at the keyboard.

Why play it: An ideal choice for two players at one computer who want to solve puzzles that require teamwork, not just fast fingers.