The last software side project I built and launched is a simple iOS app that you can find here: https://www.zone2.app
I came up with this project the same way that most come to me: I solved a problem that I had and then polished it enough that I could release it publicly. I also wanted an excuse to learn SwiftUI and it felt like a good place to do that.
I haven't made much money off of it, but that's fine because I really only built it for myself.