Interval training is the next big thing: not only is it fun, but its also a good way to make cardio sessions more efficient. Eight-Twelve is a simple yet powerful, clean, playfully animated timer app adopting the 8-seconds-sprint-12-seconds-recovery interval training pattern suggested by Boutcher et al (2013).
But thats not it. Eight-Twelve also offers other common interval training (Tabata & Little) and makes sure you get proper warming up and recovery sessions. Plus, it keeps track of your workouts and help you manage your progress.