Nice - but from a few years ago and perhaps moribund now? “An as yet unnamed project which aims to bring a pre-emptive multi-tasking graphical operating system to the 8-bit Atari.”
This really is an OS, and not just a graphical shell - even has its own filing system. Pre-emptive multitasking, message passing, glorious 1-bit windowing system with lots of fonts and widgets:
GUI | Atari8
Here’s a demonstration:
via ClaudioM on the fediverse