O2 brings professional freediver training to your pocket. Unlike generic breathing apps, it uses real CO₂ and O₂ apnea tables - the same methods used by competitive freedivers to safely extend breath holds Features: • Adaptive training based on your personal best • CO₂ tables (fixed holds, decreasing rest) • O₂ tables (progressive holds, fixed rest) • Box breathing and relaxation exercises • Progress, streaks and stats • HealthKit integration • Safety-first approach with guided warm-ups