Some of mine:
- a simple real time location sharing app[1] -- all the alternatives at that time were either clunky, with time limits, designed just for driving or with horrible privacy issues
- an SMS app for when the Nexus 7 2013 tablet was still relevant[2] -- google blocked all SMS clients on that device for some reason until Android 6.0, but I managed to find a workaround
- a way to find out the real network operator of any mobile phone in Romania[3] -- when you switch operators, you have the possibility of taking your phone number with you, so you can't rely just on number prefixes for lookup
[1] https://play.google.com/store/apps/details?id=com.emilburzo....
[2] https://play.google.com/store/apps/details?id=com.emilburzo....
[3] https://play.google.com/store/apps/details?id=com.emilburzo....