EDIT: Since you are looking for something like wxSkin , first why not use it first?
Then, if you do not want to use wxSkin, look at Juce. The purpose of Qt is not themed graphical interfaces, although masks and window style sheets are a way to implement them. There is a QSkingObject project on Qt-Apps.org , but the last time I checked it, I found that the quality of the code was poor (of course, this is subjective and reasoned).
You can see Juce , which has a dual license: GPL and commercial.
Qt (LGPL) has styles for widget styles, but it still allows the operating system to draw windows, unless you instruct it to draw frameless windows and draw decorations yourself.
, . Songbird ( XUL), . , .