A free app for Android, by Fitness Everywhere.

HIIT is a form of interval training, a cardiovascular exercise strategy that combines intense anaerobic exercise with brief periods of light activity. The goal of HIIT is to increase a person's cardio-vascular fitness, improve their ability to perform work-outs at a higher intensity, and improve their ability to perform an exercise for a longer period of time. The way HIIT is performed is by alternating short periods of intense anaerobic exercise with less intense recovery periods.

This is a free app, and you can use it for practice. You don't need any equipment to use it. You can download it and use it at home.