I'd vote for a version of Forth. Forth has fallen out of favor these days because it works best when you don't really have an operating system as such and so th

I'd vote for a version of Forth. Forth has fallen out of favor these days because it works best when you don't really have an operating system as such and so the Forth system can become the OS. And because it's arguably not that maintainable with large systems, I suppose. But on 8-bit systems running at low clock speeds like in the 1980s it was ideal. It ran quickly and used little memory. And unlike other development systems of the day there were freely available Forth systems that were public domain software and you could legally obtain them from a friend or from companies that could sell you copies for the price of the disks themselves. On the Apple II, my favorite Forth was Mad Apple Forth created in Madison, WI and which used to have a user group for it there.