Also, what programming environment are you using? Many of them bring along a lightweight UI toolkit of their own (anything from Microsoft, of course, will be pushing you towards Windows and .NET), which tends to be pretty system agnostic and static, though they often don't have RAD tools — though for anything with those other requirements you list, I've typically found the RAD tools to be more fiddly than just doing it in code (extra files, separate bindings, and a lot of extra allocations and fluff that wouldn't otherwise be necessary). You mention Qt, so probably C++ or it's ilk, but figured it was worth asking.