Worn Out is a free iPhone app developed by Dollar Shop LLC, designed specifically for runners to keep track of the mileage on their running shoes. With this app, runners can easily break in their shoes and determine the optimal pair to use on race day.

One of the key features of Worn Out is its seamless integration with HealthKit. The app automatically pulls running data from HealthKit and applies it to the default shoe. This allows users to effortlessly track their mileage without manual input.

Assigning runs to specific pairs of shoes is also a breeze with Worn Out. Users can simply open the run or shoe details and assign the run to the correct pair. This feature ensures that runners have an accurate record of the mileage on each pair of shoes they own.

Worn Out is a must-have app for serious runners who want to keep their shoes in top condition and make informed decisions about which pair to use for their races. It's user-friendly interface and seamless integration with HealthKit make it a valuable tool for any running enthusiast.