WxWidgets. (I'm guessing here that the biggest thing is the UI.) Cross platform, and likely with bindings for your favourite language, and a native look & feel. Make sure that the rest of your code is platform independent, and you're done. Also recommended: use VirtualBox to test under Win/OSX.
If you're writing in python, you probably don't even have to worry about it. (Just use the os.path module properly.) I've done this myself and it's worked a treat.
I like this idea, and I like python. Can I rely on non-technical users having python and wxwidgets installed? or is there some way to bundle everything together?
If you're writing in python, you probably don't even have to worry about it. (Just use the os.path module properly.) I've done this myself and it's worked a treat.