I have at least eight different GUIs implemented in Squeak and also native Xwindows, macOS, iPhone and Windows. Plus several through the FFI interface. And three/seven Web GUI interfaces. We used to run (around 2009) Squeak on more platforms than Linux, they all still work in the 32 versions. I'll make the old bitrotted GUI's work again in the latest Squeak 6.1 if you pay me a few thousand euro's.

I count many more native GUI support in all Smalltalk versions https://github.com/jeceljr/SmalltalkSurvey

Squeak goes back all the way to 1972, we ran on most GUIs in existence. Smalltalk was the invention of the first GUI. https://smalltalkzoo.computerhistory.org

See many of my old comments on my 18 years on HN https://news.ycombinator.com/threads?id=morphle

I even have the most scalable (massively parallel) GUI written in a few thosand lines of code: https://youtu.be/f1605Zmwek8?t=3100

And several 3D GUIs https://www.youtube.com/watch?v=1s9ldlqhVkM&t=4s and the highly scalable https://www.youtube.com/watch?v=uQTeWJNkylI