Jerboa and Eternity are native Android apps (the first uses modern technologies like Kotlin and Jetpack Compose, the second one has a lot of Java code and the UI is made with XML layouts for activities/fragments);
Voyager is portable web app built with React in Typescript, with mobile flavours made using Ionic capacitor;
Thunder is a cross-platform app built with Flutter in Dart (like Liftoff and Lemmur were in their days);
there are other FOSS apps like Combustibile (native/Java+XML) or Muffed (Flutter)...