This app was mentioned in 3 comments, with an average of 2.00 upvotes
I made an altimeter app on both iOS and Google Play:
https://itunes.apple.com/ml/app/myaltitude-lite-gps-altitude/id1146280491?mt=8
https://play.google.com/store/apps/details?id=com.badhumansoftware.myAltitude&hl=en
I make like $1 a day lulz.
I make like $1 a day off ads on one of my apps lulz
https://play.google.com/store/apps/details?id=com.badhumansoftware.myAltitude&hl=en
https://itunes.apple.com/us/app/myaltitude-lite-gps-altitude/id1146280491?mt=8
Depends what you're going for. I make like $10 a month from these apps and they're so simple. I literally just hit the GPS API on your phone and display data and ads. I used Ionic/Cordova/Angular. There is also similar compilers.
myAltitude Lite https://appsto.re/us/ROTueb.i https://play.google.com/store/apps/details?id=com.badhumansoftware.myAltitude&hl=en
mySpeed https://play.google.com/store/apps/details?id=com.bryanlopez.mySpeed&hl=en