haruspex: *bzzzzzt*, wrong. It’s easy to wish for one, but imagining working, cross platform UI is not easy. It’s actually impossible, since every platform has its own UI, and that’s the thing users notice first. Pretending there aren’t any quirks involved in UI is cheating on yourself – UIs are almost exclusively platform specific quirks. Do I use wizards or not? Tab view or list or buttons? Button order A or B? Instant apply or explicit apply? DnD or dialogs? How to present preferences? Does platform use box model or fixed widget positioning? Are widgets themeable? Is widget set closed or extendable? Are there common dialogs for X? Does platform have Tree widget ready available or not? How are icons styled? What color palette to use? Do I use icons at all? And so on, ad infinitum.
Each of these questions you need to answer, and you can be sure you’ll get every possible answer, depending on target platform. TAINTACPUI – There Ain’t No Such Thing As Cross-Platform UI.