It is intended for use by transgender men and other gender-nonconforming individuals, who bind their chest. If you have any questions about chest binding, here's the buzzfeed article for you: http://goo.gl/E0eacZ

The purpose of this app is to help people wear their chest binders the minimum amount possible, as they are somewhat dangerous to wear for extended periods of time. There is timed-based functionality which will remind you in the morning to set your binder as being on, and from that point will remind you to stretch every X number of hours and then to take off your binder after X number of hours.