I've been building a small graphical OS from scratch and the retro half of it is probably more at home here than anywhere else, so here it is.

The XT build. 8086 real-mode assembly, boots from a single 1.44 MB floppy or from a CF card on an XT-IDE (FAT12 and FAT16, read and write). CGA 320x200 four-colour desktop with a mouse, overlapping windows and cooperative multitasking, and a VGA mode where the card allows it. It ships with Sys Info, a file manager, Notepad, Paint, a four-channel tracker, a music player, Clock, Settings, a Tetris (Dostris), a Pac-Man, and OutLast. No FPU needed, no EMS, no DOS underneath: it owns the machine from the boot sector up.

Tested on real hardware across 8088 to 486, including a PS/2 L40 and, at the other end, an Eee PC. The cycle-accurate 8088 build has so far only run under MartyPC with GLaBIOS and the XT-IDE universal BIOS, never on a physical 5150/5160. Which is my ask: if you have a real XT, a 286 or an odd 386/486 chipset, I would love a boot report, good or bad. The floppy image is unodos-144.img on the release page.

The modern build.
The same OS family, forty years of hardware later: an x86-64 build that boots BIOS or UEFI from one hybrid image on most PCs made since about 2007, with its own AHCI/NVMe/USB/network drivers, a TCP/IP stack, a browser, an Office 97-style suite that opens real .doc and .xls files, and UnoAmp, a Winamp 2 clone that loads classic skins. It has a Windows 3.1 theme, which felt mandatory. Secure Boot has to be off. Other ports of the same tree run on the Amiga, C64, Mac Plus (on a real SE), NES, Genesis and a few more. I've tested NES, SNES, and a few other unusual systems you wouldn't expect to be able to run a graphical OS, using real hardware. Would love reports of this running on real hardware, as currently many other platforms have only been tested on emulators so far.

Links: the 8088 build booting on real hardware a year ago:
https://www.youtube.com/watch?v=QjB2LECJLTE
the modern build, 8-minute tour: https://youtu.be/OCIYLjtTpu8
boot the modern one in a browser tab to try it yourself (without having to write an image to disk): https://unodos.arinbakht.com/try/

Source and all the images (MPL 2.0):
https://github.com/hmofet/unodos/releases/tag/v3.35.0 ·

What runs where:
https://github.com/hmofet/unodos/blob/master/PLATFORMS.md

I built this by directing AI coding agents, and I did not handwrite the code. I know how many of you feel about that. The source and the unsquashed commit history are public, so judge the results and not just the process. I am happy to answer anything about how it was done, including the many, many things that went terribly wrong before I finally got something right.