This app was mentioned in 3 comments, with an average of 1.00 upvote
This is Strike Clock.
Not nearly as much functionality as your app, but a really minimalistic, elegant design.
What I meant was that you could use notification sounds and songs from your own phone as sounds inside the app. Having Muay Thai music is really cool, but I imagine most people wouldn't want to listen to it for each and every session of their regular interval training sessions.
I don't have an iPhone, but maybe someone can chime in on whether you guys have something like this: Strike Clock
The cool thing about this one is that you can start and stop the timer by getting close to the personify sensor. So you don't have to take off your gloves.
A proper workout timer with modular round and rest times so that you can have different lengths throughout a session.
A proximity sensor function to start and pause it would be cool too because it's pretty tough to use your screen with boxing gloves.
Essentially, I am really missing this and this since I switched to Windows Phone.