A personal trainer in your pocket.
Jenny Chang / BuzzFeed
Seconds (free, iOS) is a timer for interval training.
What's amazing about this timer is that you can customize the exercises in your circuit, and the app will speak the interval names aloud. Don't worry: you can still listen to your own music and hear the alerts on top of it!
The countdown is giant. It's visible in both landscape and portrait mode, so you'll never lose track of the time. Upgrade to pro ($5) to save timers for different types of workouts (7 minute, Tabata, HIIT, etc.).
Only the pro version of this app ($5) is available for Android.