This shows how advanced the Macintosh was for its time. I've tried using an Apple II for modern development, but it's too antiquated for that. The Macintosh, released just a couple years later, still seems contemporary by comparison.
Glad to see new programs being released for System 6!
He even made a version control system for the Mac called Amend, and a website to share Amend repositories, called AmendHub!
I'm also working on my Mac Plus under System 6, but I haven't finished any projects that I could share.