Ubertk (utk) is a C++ GUI toolkit that implements only widgets and their behaviour mechanics, while remaining agnostic of the underlying elementary event input or graphics output methods.

The user application is responsible for implementing a small set of graphics output functions, and for generating basic events (keypress/release, mouse motion/button), and passing them to the utk event processing function. Thus, utk can easily be paired with any graphics API or event processing loop. A sample user program using utk with OpenGL/GLUT and freetype2 font rendering, is provided as a starting point.

A wide variety of widgets are implemented, from the usual pushbuttons, text boxes, and checkboxes, to some quite uncommon ones such as a spherical rotation widget. Automatic layout is also supported through vertical and horizontal boxes.