Qt is more than a UI library, it abstracts away the platform too, from networking, to disk access, to UI. Think of it as an analogue to Chromium more than just UI.
You can use it as a simple gui library just fine. I've been using it in place of Tk for my python stuff for a while now. (Qt.py is a lifesaver) I haven't even tried their options for what I want to do yet, but it is definitely tempting.
Here's a good list of things Qt has stuff for.