広告またはサブスクリプションなしでちょうどタイマーアプリ
This app I've created for myself to have sense of time when doing something interesting. It has nothing to do with games or gameplay, just named for historical reasons. This app is basically a timer on fullscreen that has configurable thresholds, when it passes threshold, it will change color and vibrate. Its built using React Native, has no ads and source code is available(license does not allow making apps with it) here
https://github.com/burdiuz/react-gameplay-timer