Forget your Runkeeper and your Runtastic. Strava is the MacDaddy for tracking your activity on GPS and comparing it to your friends, or even the times of complete strangers over the same route. Hasn't let me down yet, unlike other tracking apps....
Formerly Lightning Bug. I was a little concerned, I've used lightning bug for months. However after a few minutes playing with the settings, it's easy to see the quality of the app has gone up and it is capable of better sounds and mixes.
Blue light is not conducive to sleep. This app applies a red filter to your screen to cancel out that light and aid sleep. This app is not made by the same team that make f.lux for your computer, though they are developing an app.
A more comprehensive sleep tracker, though to get all the bells and whistles that this app offers you will have to pay, that's not to say that the app is not worth it, it just depends on what you are looking for. 2 week full features trial on install
Into HIIT training? often you need a timer to measure the intervals (unless your following a video), but why buy one when you can just install an app on your phone that works just as well if not better?
You've probably heard of this workout, unless you've been living under a rock. It's a good starting point for those just beginning a workout regime, certain to give you a taste of what to expect before you move up to tougher HIIT routines
You are what you eat, and if what you eat is junk you're not going to get the results you want. This is an invaluable tool in any weightloss/muscle building program. How do you know what you are putting in your body if you don't track it?