My first Android app (possible still my favourite!):
https://play.google.com/store/apps/details?id=com.jingyen.blackjack This is the first game, and also the Android app I built. In retrospect, it is crazy to handle animations, transitions and other game effects using the default Android Studio UI builder, but I made it possible. It was also the first time I tinkered with advertising on my projects, which enabled me to learn how sustainable it is to be a solo developer, if I wanted to go on that path.
https://play.google.com/store/apps/details?id=com.jingyen.notes
https://play.google.com/store/apps/details?id=com.jingyen.charity
There are a couple of apps that I've built, that were never released to Play Store. That included a submission for an anti-drug abuse app competition (involving AR with ARCore!), and also some fun experiments. I might arrange it and put it on my Github someday, if I have time.