My 14y son challenged me to create an app to make him extremely rich. The app is a work-in-progress, while becoming rich will be a dream forever
Anyhow, I wanted to use Java all the way, so the app is Java+JavaFX+Kotlin, and the website is Java+Spring+Vaadin. Some benefits: data classes and some of the content can be shared (license information, libraries, legal info, etc.).
As a side-project, I also started a Java library to handle LemonSqueezy data, which seems to be a good solution to help us in the becoming-rich-challenge