Great post on how Alex had a need, didn't see anything that fit that need in the App Store, and decided to build an app. He has progressed to a subscription model, which could be excellent passive income for him, and heavily relies on user feedback to know what direction to take the app. Great stuff!
Be sure to read the 9 things that Alex did RIGHT in building and launching this app.
How I built an app that people actually use by Alex Miles