I had to have a peek if it's all just web. Apparently, no.

https://concatenative.org/wiki/view/Factor/UI

> The Factor UI is a GUI toolkit together with a set of developer tools, written entirely in Factor, implemented on top of a combination of OpenGL and native platform APIs: X11, Win32 and Cocoa.

> UI gadgets are rendered using the cross-platform OpenGL API, while native platform APIs are used to create windows and receive events. The platform bindings can be also used independently; X11 binding has also been used in a Factor window manager, Factory, which is no longer maintained. The Cocoa binding is used directly by the webkit-demo vocabulary in Factor.

Fascinating. Probably dead and no mention of Wayland, but fascinating.