UnixHelper

This page (obviously) hasn't been cleaned up yet, as there are duplicates and whatnot spread all over. For now, feel free to digest what is here - I'll update things and make it a bit more useful as I get time.

Berkeley Standard Distribution UNIX (BSD) and variants 4.2 BSD, 4.3 BSD, 386BSD.
Sequent ptx
Sequent DYNIX
SunOS
Linux
AT&T System V Release 3 (SysVR3)
UNIX
System V
BSD
Net1
OSF/1
AIX
AOS
Arix
A3000UX
A/UX
3B1
BNR/2
BOS
BOS/X
386BSD
BSD/386
Chorus/MiXV
Coherent
Consensys
CTIX
D-NIX
DC/OSx
DELL UNIX
DomainIX
DomainOS
DVIX
DYNIX
DYNIX/PTX
EP/IX
Esix
Eurix
FreeBSD
FTX
Generics UNIX
GNU Hurd
HELIOS
HP-UX
Interactive SVR3.2
Idris
IRIX
Linux
MacBSD
MachTen
MacMach
Mach386
Microport
Minix
MipsOS
more/BSD
NCR UNIX: SVR4 (4.2?)
Net/2
NetBSD
NEXTSTEP
NEWS-OS
OSF/1
OSx
PC-IX
Plan 9
SCO Xenix
SCO Unix
Sinix
Solaris
SunOS
UHC
Ultrix
UNICOS
UnixWare Release 4.2
UTEK
VOLVIX
Xenix
AIX: AIX/6000
Concurrent OS (Concurrent)
CX/UX
LynxOS
MiX
QNX
REAL/IX
RTMX O/S
RTU
Solaris 2
Stellix
Venix/386
Convex RTS
REAL/IX (AEG)
Sorix
System V/86
TC/IX
Velocity
386BSD
A/UX - Apple Corporation
AIX - International Business Machines (IBM)
ArchBSD - 4.4 BSD for Acorn RISC Platforms
AT&T System III
AT&T System V
BTOS
BSD/OS - Berkeley Software Design, Inc.
CLIX - Intergraph Corp.
Coherent
CTIX
Darwin
DC/OSx - Pyramid
DELPHI
DG/UX - Data General
Digital Unix (OSF1)(TRU64) - Digital Equiptment Corp. (DEC)
Domain/OS
DSR/NX
Dynix - IBM's enhanced enterprise class operating system.
ESIX - Esix Systems
FreeBSD - FreeBSD Organization
FreeBSD/Arm - 4.4 BSD for the Acorn RISC Platforms
HP-UX - Hewlett Packard (HP)
Harris' CX/UX
Helios
HEP-UPX
Hurd - GNU
IDRIS
Interactive Unix - Sun Microsystems
Irix - Silicon Graphics (SGI)
Linux
LynxOS - Lynx Real-Time System Inc.
MachTen - Tenon Intersystems
MacOS X
Minix
Motorola Unix R40
Motorola Unix V/88
MV/UX - Data General
NCR SVR4 MP-RAS - NCR Corporation
NetBSD
NeXT/OPENSTEP
NonStop-UX - Tandem
OpenBSD
OS/MP - (Solbournes - Operating System/Multi-Processing
OS/X - Apple
POSIX
PTX (Sequent)
QNX - QNX Software Systems Ltd.
Reliant Unix - Fujitsu Siemens Computer
Riscos
RT - Encore (Real Time Unix)
SCO ODT - Santa Cruz Operation
SCO Open Server - Santa Cruz Operation
SCO XENIX - Santa Cruz Operation
SINIX - Siemens/Nixdorf
Solaris - Sun Microsystems
SPARC64/OS
SPP-UX - Convex
Stellar(?) (Stardent)
SunOS - Sun Microsystems
Topix - Sequoias Enterprise Systems
TRU64 (DUNIX) - Digital Equiptment Corp./Compaq
Ultrix - Digital Equiptment Corp. (DEC)
UMAX V R/T
UNICOS - Cray Research
UniSoft - One of the first widely-used commercial UNIX ports.
Unixware/Univel - Novell and Unix Systems Laboratories
USG
UTS - Amdahl Corporation
VENIX - VenturCom, Inc.
Version 5
Version 6
Version 7
Xenix

Here's a snippet to clear up any confusion, taken right off of the Open Group's website (feel free to contact me to remove this if you consider it a no-no to have it pasted here, O.G.):

Who Owns UNIX^®?
You may have seen recent press articles announcing that SCO is the owner of UNIX or has licensed UNIX to Microsoft. Such statements are inaccurate, misleading and cause considerable confusion. The Open Group has owned the registered trademark UNIX since 1994. Here is what we said in response to a Linux World News article last week. Also available is a backgrounder that explains the history and reasons why The Open Group takes action on trademark misuse. http://www.unix.org/