Tcl/Tk
The most disgusting, bug-prone, alien looking shit I've ever seen. Tcl has taken the worst from Sh and Perl worlds and added its own uglinesses (such as encoding issues).
But it's available almost everywhere (I'm pretty sure you have 'wish' on your Linux) and helluva simple.
sdl
opengl
If you want a low-level GL instead of GUI toolkit.