I work on a cross-platform application that runs on both Windows and Mac.

We have a cross-platform library for business logic, and native Windows and Mac UIs.

The problem is that cross-platform UI libraries don't really let you fine-tune the UI. They're great for very rapid development with a basic, functional, UI.

If you get an "artiste" in product management, or you need to plug into Windows-specific and Mac-specific functionalities, you will need to use platform-specific UI libraries and keep your business logic platform-neutral.