For the large variety of operating systems out there. Of course, they'll run on a very large variety of architectures…

You NEED a 32-bit subsystem to run and build Box86. Box86 is useless on 64-bit only systems

Primarily targeted at ARM Linux implementations, this emulator allows the running of Linux x86-based applications on various non-x86 platforms. Works well on phones.

https://github.com/ptitSeb/box86

Strip down package features in interest of conserving storage and memory

A branch of AOSC/OS meant to run on particularly old or outdated devices, while still functioning as a modern Linux distribution. Used to great result on various particularly outdated pieces of hardware.

https://wiki.aosc.io/aosc-os/retro/intro/

See Debian.

16-bit processors: 8086, 8088, 80188, 80186, 80286, NEC V20, V30 and compatibles

Runs on a large variety of Intel IA16 architecture systems, which is mostly a bunch of really ancient devices. Very cool!

https://github.com/jbruchon/elks

An interesting old 386-era X11 supporting Unix variant.

https://web.archive.org/web/20211125161911/http://tenox.pdp-11.ru/os/interactiveunix/

https://virtuallyfun.com/wordpress/2010/02/09/fun-with-interactive-unix/

http://tenox.pdp-11.ru/os/interactiveunix/

Forked from MenuetOS, it has a very similar purpose, but seemingly a much more active development cycle, plus more applications and games.

https://kolibrios.org/en/index

An x86-based OS written entirely in assembly code, available in either 32 or 64 bit. Significant hardware compatibility on slightly older systems, may be worth considering for certain privacy or “obscure” reasons.

http://www.menuetos.net/

This operating system is written entirely in Lisp, containing a reasonable amount of applications and functions for such a constraint.

https://github.com/froggey/Mezzano

See DOS.

See NetBSD.

See OpenBSD.

a Linux kernel running directly on a palm pilot

An old attempt of putting the Linux kernel on various Palm devices, like the Palm Pilot, the Palm V, and Palm M500s. Apparently, it worked, at some time.

https://old.reddit.com/r/Palm/comments/qq0jr5/linux_2_on_palm_pilot/

as it is not an emulator

A modern attempt to resurrect the PalmOS concepts, in the attempt to create a sort of compatibility layer which allows compiling classic PalmOS apps for this x86-based system.

https://hackaday.com/2021/11/11/palm-os-reincarnate/

https://pmig96.wordpress.com/2021/09/08/pumpkin-os/

operating system, the “Photon MicroGUI”, and the HTML 3 capable Voyager Web

A version of QNX 1.4 that fits entirely on a single floppy. Remarkably capable for such a size.

https://www.youtube.com/watch?v=K_VlI6IBEJ0

A blog-based exploration of various old Slackware versions, going back to 1.01. The 2.0 files below are tied into this exploration.

https://web.archive.org/web/20171113201053/http://www.nielshorn.net/slackware/slack_old.php

A FTP archive containing all of the files within Slackware 2.0.1.

http://ftp.heanet.ie/mirrors/ftp.slackware.com/pub/slackware/slackware-2.0.1/slakware/

Even older than Yggdrasil, and it was known to be quite poor quality at times. It spurred the creation of Slackware from how bad it was.

https://archiveos.org/sls/

https://github.com/rdebath/SLS-1.02

Touts itself as the most feature-filled Linux distro that can fit on one bootable floppy disk. Implies itself as x86 only, across various architectures.

http://www.toms.net/rb/

Whether these emulators support operating systems for these consoles is unknown; it must be looked into further. Consoles without meaningful OSes are not included.

Nintendo Entertainment System – unnamed & unreleased emulator

https://www.youtube.com/watch?v=yhJOYLSDRLU https://firmwaresecurity.com/2018/07/03/super-mario-bros-nes-emulator-ported-to-uefi/

Nintendo Game Boy (Color) – UEFIboy (Plutoboy fork)

https://github.com/RossMeikleham/UEFIBoy https:%%//%%www.reddit.com/r/emulation/comments/bckjjc/uefiboy_game_boygame_boy_color_emulator_for_uefi/ https://firmwaresecurity.com/2019/04/07/uefiboy-gameboy-gameboy-color-emulator-uefi-subtree-fork-of-plutoboy/

Released during 1998, and a few versions appear to exist online.

https://old.reddit.com/r/Palm/comments/qur0in/palmos_emulator_runnning_on_windows_ce/

It’s very self explanatory; a bunch of interesting “retro” x11 utilities and tools.

https://cyber.dabamos.de/unix/x11/

A useful comparison for whomever wishes to reduce the memory load on a lower specification system.

https://l3net.wordpress.com/2013/03/17/a-memory-comparison-of-light-linux-desktops/

One of the first independent Linux distributions, coming from the same era as SLS and Slackware.

https://archiveos.org/yggdrasil/

http://www.ibiblio.org/pub/historic-linux/distributions/yggdrasil/