sworkit - a whole range of exercises and you can plug in how much time you have and it will craft a plan for you (and guide you through it). It's more than just HIIT (includes stretching!) and they different workouts based on your fitness level
Anonymous
01/17/2019 09:55
Subject: Re:Best HIIT app?
fitnessblender.com has a search function that you can filter out just the HIIT workouts.