[SLL] Alternative alternative operating systems?

[Jeremy C. Reed]

Just curious, any of you using or looking at alternative operating 
systems?

(In my definition, mainstream Linux and *BSDs are not alternative. But 
some derivative based on Linux kernel may be.)

Here are some that I have heard about over many years, but recently again:

OS/2
I saw http://www.smedley.info/os2ports/ with up-to-date software for OS/2.
As for OS/2 itself, I don't know if still maintained. I found eComStations 
(Ecs) which is based on it. http://www.ecomstation.com/. Don't know if 
open sourced.

Interix
I see it is still being used. It is Microsoft's Unix for Windows (based on 
OpenBSD I had heard). (From my own little experience with porting software 
to Cygwin, Interix is more portable.) 
http://technet.microsoft.com/en-us/interopmigration/bb380242.aspx

DragonFly
The fork of FreeBSD now over five years old. Can run kernels in userland, 
HAMMER file system for massive disks, and has goal for system clustering 
over Internet. (Disclaimer: I frequently use this and have commit 
privileges.) http://www.dragonflybsd.org/

QNX
Known for "realtime". I played with the bootable disk with browser around 
ten years ago. I see the operating system is still maintained, but I don't 
see downloads and assume is not free or open source. But I do see it can 
run open source software. http://community.qnx.com/sf/projects/pkgsrc

Haiku
Formerly known as OpenBeOS and inspired by BeOS. http://www.haiku-os.org/ 
Can run some common open source Unix software.

PureDarwin
I thought Darwin outside of Apple was dead as it was no longer maintained 
and no easy way to install. But now I see PureDarwin. 
http://www.puredarwin.org/

Inferno
Is free software. Followup of Bell Lab's Plan 9 distributed operating 
system. http://www.vitanuova.com/inferno/


Do you use any of these? Or tried any other alternatives?