Here's another lesser known homebrew OS, Snowdrop OS.
So far, it looks very promising, tinkering with it seems fun.
Has BASIC interpreter, but programs can also be linked/compiled.
Source code is available, too.

I'll let the author speak for himself here:
"Snowdrop OS was born of my childhood curiosity around what happens when a PC is turned on,
the mysteries of bootable disks, and the hidden aspects of operating systems.
It is a 16-bit real mode operating system for the IBM PC architecture.
I designed and developed this homebrew OS from scratch, using only x86 assembly language."

Link: Homepage

PS: The author's main site is neat, too! I higly recommend browsing by.
Lots of electronics projects, some of which interface with Snowdrop OS.
Examples:
- stepper motor driver controlled by Snowdrop OS
- interfacing a Nintendo NES from Snowdrop OS
- interfacing with a 16x2 LCD via parallel port

Another one, Solar OS .
It's an experimental 64-Bit real-time OS (formerly 32-Bit).
The OS is written in ASM and has a lot of development tools, it seems.

Requirements:

Only 8Mbytes RAM (even less)
P1 class CPU at 266 or even lower
Can be setup to run with under 2Mbyte RAM with some limitations.

Homepage: http://www.oby.ro/os/

Hi again, please excuse for the double post (tripple post?) here, but there's another retro OS.
It's SerenityOS, a mix of Win95 GUI and Unix architecture.
It's especially made for friends of both Windows 9x/NT and Linux, I suppose.

https://serenityos.org/

There's a thread at Vogons, which was made by me (?) - I'm a bit surprised and confused, to be honest. 😅
Re: New Linux distribution that looks exactly like Win95

Jo22 wrote on 2025-06-14, 00:20:

Hi again, please excuse for the double post (tripple post?) here, but there's another retro OS. It's SerenityOS, a mix of Win95 […]
Show full quote

Hi again, please excuse for the double post (tripple post?) here, but there's another retro OS.
It's SerenityOS, a mix of Win95 GUI and Unix architecture.
It's especially made for friends of both Windows 9x/NT and Linux, I suppose.

https://serenityos.org/

Just as I had my hopes high for an eventual Windows-looking environment to run retro games from the 90s era (if this OS would also supply tight integration of DOSEMU and Wine to run DOS/Win apps like on real Windows), I read their FAQ, and it felt largely discouraging:

Will SerenityOS support $THING? Maybe. Maybe not. There is no plan. […]
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Will SerenityOS support $THING?
Maybe. Maybe not. There is no plan.

When will you implement $THING?
Maybe someday. Maybe never. If you want to see something happen, you can do it yourself!

Where are the ISO images?
There are no ISO images. This project does not cater to non-technical users.

So it feels like someone is just having fun with this and might drop development forever at any time when they lose interest or it works "well enough" for them on their own machine.

Except if maybe someone else picks this up with a more serious and goal-oriented approach.

Not sure if this has been mentioned in the past, but I think MikeOS is always good fun!

I actually haven't tried it since version 4.5, so I have some catching up to do.

I think I have to dig this thread much deeper to get new possible OS for playing around in my multiboot-setups. https://youtu.be/uylD7rDSorg?si=QpV9D_kuXYeDZ6aP

dr.zeissler wrote on 2026-01-28, 10:31:

I think I have to dig this thread much deeper to get new possible OS for playing around in my multiboot-setups. https://youtu.be/uylD7rDSorg?si=QpV9D_kuXYeDZ6aP

Qnx 6 RTP might work on your machine, look on page 9.

For that 486/133 a bit to high (P200+) but Cloudschatze showed DR-Dos with NewDeal3 that is indeed intersting because I am still searching for an icon-based guy for dos. Testing QMIII is at first, but DR-DOS and Geos/NewDeal is second. Not a real OS for sure, but interesting to maxout the machine. Executor is also running very nice on that 486/133.

dr.zeissler wrote on 2026-01-30, 11:14:

For that 486/133 a bit to high (P200+)

I did try it in 86box with a 486 PCI motherboard and a dx4/100, it did work under that emulated machine.

But it's not a real one so I'm curious if you could try it on your 486. It installs as a loopback file under Win9x (like the Personal Edition of BeOS) so you can always uninstall easily.

Jo22 wrote on 2025-01-29, 09:53:

Not an OS per se, but a fine retro GUI for DOS - MCShellGS 97 v3.1 ! Runs on 80286 minimum w/ VGA, but needs some XMS memory (2 […]
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Not an OS per se, but a fine retro GUI for DOS - MCShellGS 97 v3.1 !
Runs on 80286 minimum w/ VGA, but needs some XMS memory (2 MB up).
Reminiscence of System 7.x..

Features: Picture Viewer (BMP/PCX), Print Manager (Epson/Laserjet/Proprinter), Virtual Memory, Calculator etc.
File Manager: Copy/Format Disk, Search Files, Copy+Paste, etc.
Desktop: Wallpapers, Patterns, Clock, Sound Effects etc.

I never knew that existed!

While also not operating systems, I spent a fair amount of time using Fusion/Basilisk II/SheepShaver to run MacOS 7/8 on my PC. I also used BeOS (later OpenBeOS, then Haiku).

And the most curious (almost an operating system) alternative I can think of, but that I can't actually remember using, is Sun Microsystems Looking Glass 3D.

https://distrowatch.com/table.php?distribution=lg3d
https://web.archive.org/web/20110223094847/ht … t/projects/lg3d
https://www.youtube.com/watch?v=c-4y0bwl6w0