The one that the most other people found useful: Remote Control Collection. It's an app that allows you to control your PC or Mac from your Android or iOS smartphone while connected to the same network. It also was available for Windows Phone and BB10 back in the days.
I've built it about 10 years ago for myself because I was too lazy to get up from the couch to control my media PC and the existing apps were all terrible to use. Turns out many people found good use for it, over 10 million across platforms by now.
I worked for NBB as an Android Engineer about 5 years ago. While refactoring the analytics / tracking services (5 different providers in the app), I noticed that customers credit card data was leaking to analytics providers. I informed my PO about this, but he decided that this wouldn't be worth the effort fixing. I left the next day.
You can, in fact, do BLE scans in the background on iOS. It's tricky and requires some workarounds, like basically everything related to background tasks in iOS.
I've built it about 10 years ago for myself because I was too lazy to get up from the couch to control my media PC and the existing apps were all terrible to use. Turns out many people found good use for it, over 10 million across platforms by now.
https://play.google.com/store/apps/details?id=com.steppschuh...