Thanks. Good to know

     I remember also a very simple toolkit called Xforms, 
http://xforms-toolkit.org/. I made a few guis with this toolkit between 
2000 and 2005. You can get started and have a running gui within a workday.

     apt-get install libforms2 libforms-dev libforms-bin libforms-doc

     Today it also has an OpenGl extension with packages libformsgl2 and 
libformsgl-dev

     Didier