Building apps was one of my hobbies in college. The following 4 apps are functional.
Music video stations using Spotify or Last.fm discovery APIs
php-MySQL based Journaling application
Fresh wallpapers for macOS using multiple sources
An adaptation of the game "Guess Who?"
These apps are no longer maintained:
Assistant chatbot that can answer general questions about you.
AutoLyrica for iTunes
Lyric app for (the old) iTunes.
NowPlaying for iTunes
Now Playing app for (the old) iTunes.
An app for monitoring your daily progress.
Chatbot for personalized song recommendations.