Compagnon HIIT is an open-source project (license MIT) aiming to provide a mobile application to help people using the High Intensity Interval Training method. Read more about this method on wikipedia.

Features:

configure your workout
use the timer
keep the history

Anti-Features:
NoSourceSince: Upstream source for this app is no longer available. Either the app went commercial, the repo was dropped, or it has moved to a location currently unknown to us. This usual means there won't be further