NUI is a GUI ToolKit intended to work with SGI's OpenGL API. It is similar in many ways to GTK+, Qt and even Win32, but with many enhancements in order to make it an easy and yet powerful tool for cross- platform GUI programming. It is currently developed on platforms supported by the NGL framework.
TacitPixel (formerly libTAP ) is a prototyping system for virtual reality and augmented reality applications. It runs on a variety of platforms. RAP (rapid application prototyping) is done through the Lua interface, which mirrors the C++ namespace as closely as possible. libTAP has a small but distinctive feature set, focused on prototyping of realtime 3D simulations.