Just Drive
I learned Lua because I wanted to make a driving game.
Before I knew much about programming, I wanted to make a game where I could drive around and collect cars. That became Just Drive, which I wrote in Lua using Roblox Studio; it has highway traffic, racing and car customization. I learned most of what I needed from documentation, YouTube and developer forums, and a lot of afternoons went into getting individual features to work. I had a working game by eighth grade, and I still think of it as one of my favorite things I've made.