Recommendation for non-DOS/Unix open source OS outside x86/X64

There's RISC OS: https://en.wikipedia.org/wiki/RISC_OS

It was written for the Acorn computers that were the original use of the ARM architecture. It's still around and is pretty lean, despite being complete with a GUI and network capabilities.

The MIT Lisp machine system: https://tumbleweed.nu/lm-3/

Mezzano, a much more recent OS written in Common Lisp that runs on Arm rather than special hardware: https://github.com/froggey/Mezzano

Inferno - https://www.vitanuova.com/inferno/

Description from Wikipedia: “Inferno is a distributed operating system started at Bell Labs and now developed and maintained by Vita Nuova Holdings as free software under the MIT License. Inferno was based on the experience gained with Plan 9 from Bell Labs, and the further research of Bell Labs into operating systems, languages, on-the-fly compilers, graphics, security, networking and portability.”

Plan 9 - one version of which is 9front, which says this:

"Multiple installation media are provided for PC, Raspberry Pi, MNT Reform, and QEMU. For PC, burn an .iso file to CD, or dd it directly to USB media. For Raspberry Pi or MNT Reform, dd an .img file directly to sdcard.

The pi.img file can be used for Raspberry Pi 1, 2, and 3. The pi3.img file can be used for Raspberry Pi 3 and 4.

QEMU images are provided in QCOW2 format."

https://9front.org/releases/

There's Niklaus Wirth's Oberon[0].

0. https://www.projectoberon.net/

RISC-V, ARM in development: https://en.wikipedia.org/wiki/Haiku_(operating_system)

https://en.wikipedia.org/wiki/AROS_Research_Operating_System

https://en.wikipedia.org/wiki/MorphOS

https://en.wikipedia.org/wiki/AmigaOS_4

https://en.wikipedia.org/wiki/Inferno_(operating_system)

https://en.wikipedia.org/wiki/Illumos

There have been a number of passes at embedded Smalltalks. Eg. https://hackaday.com/2020/07/12/making-smalltalk-on-a-raspbe...

Back in the day, Tek oscilloscopes ran ST on the metal.

Are we to assume you want it to run on actual hardware? I imagine there are a number of OSes that qualify if emulation is acceptable. One I like:

http://www.vm370.org/

Full S/370 assembler source included.

Technically you can run Redox-OS on a Raspberry Pi 3 B+ (ARM), but it still works best on x86_64: https://doc.redox-os.org/book/raspi.html

If you decide you miss DOS, then you can also use the DOS emulator available on Redox-OS. It's not Linux but there are some linux-inspired stuff there, including apps from the Cosmic desktop environment. Both announced here: https://www.redox-os.org/news/release-0.9.0/

https://fuchsia.dev/

XINU (Xinu Is not UNIX) OS…good book on it too for Operating System design!

https://xinu.cs.purdue.edu/

I've got a hobby OS that's currently x86 32-bit only. amd64 and arm64 are on my roadmap, but if all goes well, it's going to be the same experience on all three platforms, so arm64 won't be anymore exciting than x86 32-bit. Other than, you could run it on a raspberry pi or maybe an arm apple.

I imagine most hobby OSes are looking at arm support vs adding something else, and arm support is going to be more fiddly and have less to show for it. I haven't found much time to work on mine lately, but other things are way more important like getting my virtio-net driver and the v86 virtio-net device to work together; having networking in https://copy.sh/v86/?profile=crazierl would be really neat. Running on a pi would be neat too, but a browser demo is way more accessible.