Red: A programming language inspired by REBOL

I remember looking at red ages ago but never got round to using it. I like to learn odd non-mainstream languages. Currently learning Nushell which is an amazing alternative shell. And I like the look of roc-lang too.

I'm desperate for a truly cross platform programming language with gui abilities on those platforms. I'm slowly learning dart/flutter for this but truly wish for something simpler. I get the reasoning behind flutters declarative style but it's certainly not simple, especially when you get to state management.

Tcl/tk is still alive and doing well. It's cross platform, very quick to learn, and easily embeddable into other languages/projects.

Can you name an important software written in Tcl or Tk?

Important softwares written in Ruby for example include Rails and Homebrew.

Tk has been embedded in python as the GUI toolkit since at least 2.x days. It's used for IDLE, the IDE shipped with Python, and is also used for the turtle module's graphics.