Fireboy and Watergirl is a popular game series developed by Oslo Albet. The games feature two characters, Fireboy and Watergirl, who must work together to solve puzzles and overcome obstacles. Here are some of the most popular Fireboy and Watergirl games:

1. Fireboy and Watergirl in the Forest Temple: This is the first game in the series, where Fireboy and Watergirl must navigate through a temple filled with obstacles and traps.
2. Fireboy and Watergirl 2: The Light Temple: In this game, Fireboy and Watergirl explore a new temple filled with light-based puzzles and challenges.
3. Fireboy and Watergirl 3: The Ice Temple: This game takes place in an ice temple, where Fireboy and Watergirl must avoid icy hazards and solve puzzles to reach the exit.
4. Fireboy and Watergirl 4: The Crystal Temple: In this game, Fireboy and Watergirl must work together to collect crystals and navigate through a new temple.
5. Fireboy and Watergirl 5: Elements: This game features a new storyline and includes four different temples based on the elements of fire, water, wind, and earth.
6. Fireboy and Watergirl 6: Fairy Tales: is the sixth game in the Fireboy and Watergirl series.This time, the duo find themselves in a magical forest filled with fairy tale creatures and enchanted objects.
   
   The game features new levels that are inspired by popular fairy tales, such as Cinderella and Rapunzel. Each level presents unique challenges and obstacles that require the players to use their problem-solving skills to progress.
   

These games are available to play for free online and have become a popular choice for gamers of all ages.