What I'm looking for is a clear and consise description of a strategy for developing a custom designed user interface that will be easy to port across to different platforms. I have a some experience in developing Windows apps and that will be my initial choice of platform, but I want to make sure that if it becomes necessary, I can easily port my application across to Unix and other platforms (of which I have very little experience of, hence this question). I'm guessing that developing anything in MFC is a bad move right?!!
So what do people recommend? I'm just asking for an outline of the strategy, and maybe links to any resources that people would think I would find particularly useful.