OK, so question time: I haven't done any Java (let alone Kotlin) coding now for what seems like ages, but will need to implement a relatively simple, yet cross-platform client for my upcoming application. It will probably sound extremely silly, but were I to write a GUI that speaks to a REST API, where should I start doing my research?
If you have more recent experience on C++, Python or Javascript then you should be looking into Qt, PyQt, Electron (respectively) or other alternatives first, but if you're willing to try the Java environment you could look into the following components to get you started:
-Kotlin to speed up development
-Gradle as a dependency manager
-Retrofit + OkHTTP to create a type safe backend API definition
-JavaFX for the GUI components
-Gluon's scene builder if you like creating your FX views in xml, with a visual editor
-RX as a powerful library for async tasks
-Gson or Jackson as a JSON parsing library
-IntelliJ if you like coding with IDEs, for its massive refactoring capabilities
It's a lot to take in if you're unfamiliar, but together they all come to form really solid desktop applications.