However, as an old fogie, I recall a craze back in the 70s and 80s called 5BX, which stood for 5 basic exercises, created by Swedish aircrew iirc. The reason I recalled it is the mention of rapid-style jumping jacks and push ups in the 7-minute workout. 5BX had increasingly quickened routines for jumping jacks (from a crouching position), sit-ups and push-ups (with claps thrown in as you completed each push-up).
All of this worked very well in terms of actually toning your body, getting a good daily cardio workout, and a sense of fitness... until it did irreparable back and other damage to quite a few people. So just be careful, especially if the high intensity and the 7 minute time limit drives you to a regimen that gets anywhere close to a 5BX style work out in terms of quick, jerky movements.
Personally, I've reverted to playing basketball like I did in my college days, with high intensity worked into it with repeated lay up, jump shot routines, etc. It's working great for cardio and overall body toning. I would like to do weights as well, as there is a body of evidence pointing to its value, but basketball is plenty far for me at this stage.
This is a good free one I use myself:
https://itunes.apple.com/us/app/interval-timer-seconds-by/id...
https://itunes.apple.com/us/app/gymboss-2-interval-timer/id5...
https://play.google.com/store/apps/details?id=com.halcyoni.g...
The main problem is that the standard timer app on iOS only acts as a stopwatch...so the final ten seconds of each interval, I'm watching the clock so that I can hit "Lap" and move on...this is awkward when I'm also wearing headphones to listen to music.
What would be ideal for me is to have a simple timer that would alert me when the interval was done and automatically move on to the next one....like a repeating event on a calendar. I'm sure there's an app for that but I just didn't feel like downloading a bunch and doing trial and error.
One more twist: I can't do all the exercises in the 7-min workout (as made famous in the NYT)...jumping jacks would annoy the shit out of the people below me. So I make up my own. A timer that would allow me to set up my own sequence would be fabulous.
Anyway, this is just a longwinded way of saying that there's a need for a niche app here, and it would definitely be a fun coding project...I'm glad someone else thought of it first :)