As a kid I went from basic to assembly. When I was shown Forth by my dad's friend I was totally caught up in Forth on my C64. I later tried Pascal which is also great but it wasn't close to forth in my mind. It was awesome Except you had to pay for the language and I am guessing that is why it died.

Currently my preferred language is Racket because it is so fun and practical, reminds me of the earlier days of Python but much more thought out. You write you code (which is fun) and you have an executable all within one setting.

Armed with that and a copy of Threaded Interpretive Languages by Loeliger (How I found out about the book is beyond me) from the library I managed to put together a complete(ish) Forth for the Apple ][ running ProDOS.

I think the magic bit with Forth is that it's easy to see how to write one by the time you've finished Starting Forth.

Is it though? Man, maybe I'm dumb :)

I wish there was an easy checklist: Create stack data structure, create return stack, create primitives ...etc.

What does Factor have to do with my question? Yes it's a concatenative language that is still maintained although Slava left. I'm guessing it wouldn't make a great example if you're suggesting going through source.

And it seems to be free for personal use: https://www.forth.com/starting-forth/