What other operating systems do you know about?
 

I guess most are familiar with the Windows, Mac, Unix family... maybe ATARI, Amiga, and maybe even BeOS.

But every now and then I stumble upon one that I never heard about... that quite possibly shares developer and userbase for the most part, but is nonetheless exciting to look into.
Like:

http://www.kolibrios.org/
http://www.reactos.org
http://www.haiku-os.org/
http://www.freedos.org/

I think some of those might become quite interesting. I haven't used any of those outside virtual machines and I can imagine they might have a hard time with real world hardware, but I think there is definitely a potential there.

Does anyone know more about those, or maybe even other ones?

I cut my teeth in the 70s on Burroughs operating system. Then there was Wang, which was really a sort of knockoff of IBM. And then there was ACP/TPF where the money was. I did a bit of BAL programming on an IBM370. Along the way, there was Coherent, which was an extremely low-budget and limited version of Unix. Is that enough? :)

Wikipedia has a list if you just want a list.

AppleDOS (Apple-II)
Vax VMX
Unix
....But so what?

1968, working as a summer intern, n the group developing the B6500. I remember being totally impressed at the Adder module, which could add 2 64-bit numbers in one clock cycle at 1 MEGAHertz.
The logic family (ECL = Emitter-coupled logic) was flaky beyond belief. Integrated circuits----what's that???

MenuetOS? Not windows like and not nix either.

HP-2000 Access BASIC
HP-3000 MPE
IBM/370 VM/SP, VM/XA, MUSIC/SP, VM/HPO, MVS/XA aka Z/OS
Dec VAX
AIX
UTS
RSTS-E
Data General something-or-such
AppleDOS and Apple ProDOS
TRS-80
KEX
CP/M
MS-DOS
Commodore 64
Commodora Amiga (yay!)
Apple System-X
Apple OS/X
Windows
Linux (Red Hat, Suckware ;), Gentoo)

Savin' the best for last ... ;) Did I miss one? Oh, probably...

Yep, you missed at least one. I earn my bread and butter on IBM OS/400.

One that I can't seem to find on the 'net is EOS ("Elementary OS", not the same as the one used for supercomputers) for the ColecoVision ADAM.

CDC-6500 NOS/B
IBM360 JCL
Perkin-Elmer RTOS
AppleDOS
TRS-80
PDP-8 Assembler
PDP-11 Assembler, RT-11, RSX-11
JOVIAL J73 (combination OS/programming language for embedded military computers)
ADA (see above)
CP/M
VAX VMS
Atari 800
Amiga
VRTX
Rainbow OS
TI DSP with Code Composer
IBM Series/1
Mac System 7
System V

There are some others. I don't recall right now.

Maemo, Nokia OS (/ISA)..

I don't know most of those listed in above posts, and haven't heard about all of them..but it just happened in the summer that I got interviewed (trough phone - I didn't even know they still do it, with web existing and all) by a guy for some public research, and among other things in the survey he asked what operating systems I knew, had used or would be willing to use at work if I could choose. The funny thing was, this guy was apparently using a "pick-from-a-list" interface for recording the answers, and the predefined selections of course didn't contain more than two or three of my answers..well designed software that it was, he couldn't add "extra" answers there because it wasn't an "open question" -- there were only radio buttons or something like that -- so he started writing down with a regular, physical pen, asking me to spell a couple of the names I mentioned letter by letter as if he had never ever heard about them :) I don't know all the rare operating systems either, but it struck me a little odd that he didn't even recognize Linux (in general) nor the BSDs for example..all he had was Windows, SuSE, RedHat and OS X (those he knew, as they were on the list on his screen - "wait..yes, here it is..*click*") and whatever he (mis)typed on the paper..

I hope they had just upgraded all their applications, hadn't had time to practise using them, this guy had a selective memory loss and some bad luck, because it didn't really feel as smooth as one could expect a public survey to be :)

I was more hoping to find people who used some obscure OS and want to share their stories. Even with the living projects it's hard to find information on what their target actually is. It's more a "here's svn, check it out for yourself... any questions?" kind of thing.

Old operating systems
 

I've looked at some of the new ones, like Haiku and Syllable, but even when they are finished I can't see that they can offer anything that you can't get from Linux. I suspect that their chief value is as test-beds of new ideas on OS design. In fact, I think that is the motivation for Plan 9.

Old ones, however, can be a trip down memory lane. I can play Sopwith on FreeDOS and remember running it on an original PC. I can also remember things like Peachtext, PFS, edlin, autoexec.bat - what a relief they're all behind me!

QDOS, the QL OS, still comes in useful and runs under QemuLator running under Wine. I have some software I wrote in SuperBasic for QDOS that I could never be bothered to convert to FreeBasic or whatever, and a complex spreadsheet program where I can't remember how the formulae work, let alone see how to convert them. Today I've used a database as a result of my failure to get OpenOffice Base to work: the 1980s to the rescue! I also use a QL text editor for things that can't be done in Gedit or OpenOffice, like transposing tabulated columns. I've always liked QDOS: a robust, multitasking command-line system that wasn't too complicated. As you may know, Linus chose a QL in preference to the 6086 PC and learned a lot from disassembling QDOS. I seem to remember he used the task prioritising algorithm he found there.

I really feel I've missed out on a lot by only getting interested in computing five years ago...I could kick myself. Ouch!

IBM 360 DOS
Four-Phase Systems IDOS
Four-Phase Systems MFE
Atari TOS
CP/M
DEC VMS
Unix (Multiple flavors)
Ultrix
PC-DOS
MSDOS
OS/2
Xenix
DSC Nexos
VRTX
QNX
uCos
VXworks
Linux

and lastly... Winblows