TkInter (!) ;)

This is a GUI used by several programming languages, like Python - it is used heavily on Linux systems (as Tcl/Tk).

And that's correct.  It isn't that the developers were afraid to use it on MacOS, but that it wasn't supported.

C makes it easy to shoot yourself in the foot. C++ makes it harder, but when you do, you blow your whole leg off.

 -- Bjarne Stroustrup

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