GtkGLExt is an OpenGL extension to GTK+. It provides additional GDK objects which support OpenGL rendering in GTK+, and GtkWidget API add-ons to make GTK+ widgets OpenGL-capable.
Xgdk is a Cross-Platform Game Development toolKit. Its purpose is to provide a set of easy-to-use and extendable libraries for rapid development of 3d interactive applications such as videogames, demos and prototypes.