Good old Tcl. Man, that language just absolutely refuses to die.
I remember learning in sometime in the 90's specifically to use Tk for some personal project or another. What a weird language. Pathologically dynamic where everything can be (re)defined at runtime, including control structures; "stringly" typed, so everything's a string; you can get at the variables in functions higher up the call stack, effectively "transforming the call stack into a call tree".
It's interesting to see that it's still alive and being used, and that TkInter is apparently "a thin object-oriented layer on top of Tcl/Tk.".