I'd just like to add a few things that should probably go into the "Technical Discussion" section: *) Dialog Button alignment and ordering Mac OS dialogs have the OK button in the lower right corner, and the Cancel button to the left of it. Most other platforms have it the other way round. Buttons in the wrong place could be very annoying to the end user, so some abstraction is needed here. *) Dialog Button naming A rather minor point: many platforms have ready-made Yes-No-Cancel dialogs. Apple expressly forbids "Yes" and "No" as button labels - they recommend using verbs ("Don't Save" - "Cancel" - "Save") instead. Might be too much work to bridge these differences, but who knows? *) File types Nowadays, MacOS applications are allowed to use extensions instead of the traditional Mac-specific metadata, so it is probably not a big issue. *) Displaying File Names and Extension Hiding Both Mac OS and Windows have an option to hide file extensions (the semantics differ in the details). Mac OS also has a feature where every file or folder on the disk can have a (possibly localized) "display name". For example, when the system language is set to German, the folder whose POSIX path is /Applications/ is displayed as "Anwendungen". It's probably too early to discuss these details yet, but I thought I'd mention them before they get overlooked. Cheers, Wolfgang