FileCensus/FCSpaceMap ? reverse-engineered prompt

Build me a desktop app that helps people see what is using up disk space on their computer.

I want it to let the user pick a drive or folder, scan it, and then show an interactive treemap where bigger files and folders take up more space on screen. It should be easy to hover over items to see details, and there should be a way to toggle free space on or off and filter the view so it is easier to focus on certain files or sizes.

Please make it work on Windows, macOS, and Linux, with a native looking interface. It should also choose good system fonts automatically depending on the platform and language, and support a dark mode title bar if possible. Keep it simple and polished, and if you need to look up current docs online while building it, go ahead.