Car Tracker
Who took which car, and when it's coming back
Android 
Expo 
React Native · React Native Maps 
Convex For households with more drivers than cars: Car Tracker records who took each car, why, when they expect to be back, and where it is now. No more group-chat archaeology before every errand.
It runs on Expo and Convex with live location, push notifications, and Android home-screen widgets. It ships privately to the family as signed APKs — which is exactly the audience it was built for.