SDL_sif is a simple addon library for SDL for defining areas in which to catch events. Areas can be everything from simple rectangles and polygons to combinations of more advanced shapes, like union, difference, and so on. Once an area is set up, you will receive SDL events with information about what happened where.
KaiView is a GUI toolkit/framework for writing applications using the TOM programming language. Based on a vector-oriented drawing layer using libart and freetype2, it provides a widget layer with subject/view separation, forms loaded from XML files, live updates to the GUI, Unicode support, abstract manipulator classes, antialiased everything, and a lot more.