Fifteen years ago, the modern parts of the Pixar animation system used Tcl/Tk for the GUI. The older code looked like Tektronix 4013 displays... I didn't work on GUI code much, but what I did do was fun. Since this was an internal application only, it didn't have to look slick and modern, it just needed to have all of the features required by Production and be reasonably fast and reliable.

I have no idea what the software looks like now.