Among the many rumored features for Apples upcoming iOS 8 is Healthbook– The companys first major foray into the world of in-depth health and fitness tracking. While this app provides common statistics such as heart rate and calories burned, it takes things a step further by measuring your sleep, blood sugar and even your hydration level when youre in the middle of an intense workout. Healthbook will likely be a key selling point of the iPhone 6, which will also reportedly be able to monitor the humidity and temperature.