TGUI is an easy to use cross-platform c++ GUI library for SFML.
The gui is easy to use, with only a few lines you can e.g. have a fully functional TextBox on your screen. The widgets can be created by just using colors or by using images, making the look very customizable. You can also add custom widgets and change parts of the loading process of the widgets.
TGUI will work on all platforms that SFML supports. This means that you can use it on Windows, Linux, Mac OS X, FreeBSD and experimentally on Raspberry Pi, Android and iOS.