Gnok.io was my first completed solo game. It's still running at http://gnok.io and available on the App store and Google Play store.
In the game you shoot a marble at other marbles to try and hit them out of the arena. Damage builds up from hits and makes you fly further when you get hit again. It's fun!
Each Game Server can support ~1000 concurrent players and has 100 AI constantly playing forever to make playing possible with a low to non-existent playerbase. Unique IDs are generated for whatever device you play on and you earn points for playing and logging in that can be used to unlock cosmetics.
It's like a real game just not well designed and with novice programmer art :]