I would also say that wxWidgets makes it pretty easy, particularly as you have the source. I know there is a mass of #defines in it etc. but I have found it very useful and reliable across the 3 major platforms (Win, Linux, Mac). And it renders natively on them, unless you force wxUniversal (which does its own rendering of controls, like Qt does). I would even argue that Qt does a worse job of making stuff look native, particularly on Mac OSX; wxWidgets controls are native on Mac OSX, as underneath it is Obj-C mm files everywhere.