Gui library for game

I'm making a game with OpenGL render api. Now I need in level editor. It should consist of lots of widgets parents/children etc, so it's hard to write need widgets by hands. Any ideas about good gui-system which can be easilly connected with opengl? The most important part is gui editing. I really need some editing-tool for it.

Thanks

What is a GUI in games?

The GUI (/ˌdʒiːjuːˈaɪ/ JEE-yoo-EYE or /ˈɡuːi/ GOO-ee), graphical user interface, is a form of user interface that allows users to interact with electronic devices through graphical icons and audio indicator such as primary notation, instead of text-based UIs, typed command labels or text navigation.

You should have a look to http://qt.nokia.com/ .

It is very easy to inject the OpenGL rendering into Qt widgets.

To easily edit your GUI, you can use Qt Creator ( http://qt.nokia.com/products/developer-tools ).