The history of UNIX is very interesting and this UNIX History page by Éric Lévénez is very cool, check it out:

UNIX History by Éric Lévénez

Reproduced with Éric's permission, here are some of the UNIX variations in his history chart:
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<td width="25%">
1BSD<br>
2BSD<br>
3BSD<br>
4BSD<br>
4.4BSD Lite 1<br>
4.4BSD Lite 2<br>
386 BSD<br>
Acorn RISC iX<br>
Acorn RISC Unix<br>
<a href="http://www-1.ibm.com/servers/aix/">AIX</a><br>
AIX PS/2<br>
AIX/370<br>
AIX/6000<br>
AIX/ESA<br>
AIX/RT<br>
AMiX<br>
AOS Lite<br>
AOS Reno<br>
<a href="http://www.apple.com/appletv/">AppleTV</a>
<br>
ArchBSD<br>
ASV<br>
Atari Unix<br>
<a href="http://www.applefritter.com/ui/aux/">A/UX</a><br>
BOS<br>
BRL Unix<br>
BSD Net/1<br>
BSD Net/2<br>
BSD/386<br>
<a href="http://www.windriver.com/products/bsd_os/index.html">BSD/OS</a><br>
CB Unix<br>
Chorus<br>
Chorus/MiX<br>
Coherent<br>
CTIX<br>
CXOs<br>
<a href="http://developer.apple.com/darwin/projects/darwin/">Darwin</a><br>
<a href="http://www.debian.org/ports/hurd/">Debian GNU/Hurd</a><br>
DEC OSF/1 ACP<br>
<a href="http://www.desktopbsd.net/">DesktopBSD</a><br>
</td><td width="25%">
Digital Unix<br>
<a href="http://www.dragonflybsd.org/">DragonFly BSD</a><br>
Dynix<br>
Dynix/ptx<br>
ekkoBSD<br>
Eunice<br>
<a href="http://www.crescentanchor.com/products/FireFly/">FireFly BSD</a><br>
<a href="http://www.freebsd.org/">FreeBSD</a><br>
<a href="http://freedarwin.foxybanana.com/">FreeDarwin</a><br>
<a href="http://www.gnu.org/software/hurd/">GNU</a><br>
<a href="http://www.gnu-darwin.org/">GNU-Darwin</a><br>
<a href="http://gnuppix.org/">Gnuppix</a> <a href="http://www.gnu.org/software/hurd/hurd-l4.html">GNU/Hurd-L4</a><br>
HPBSD<br>
<a href="http://www.hp.com/products1/unix/operating/index.html">HP-UX</a><br>
HP-UX BLS<br>
IBM AOS<br>
IBM IX/370<br>
Interactive 386/ix<br>
Interactive IS<br>
<a href="http://www.apple.com/iphone/">iPhone OS X</a>
<br>
<a href="http://www.apple.com/ipodtouch/">iPod OS X</a>
<br>
IRIS GL2<br>
<a href="http://www.sgi.com/developers/technology/irix/">IRIX</a><br>
<a href="http://www.linux.org/">Linux</a><br>
Lites<br>
LSX<br>
<a href="http://www.apple.com/macosx/">Mac OS X</a><br>
<a href="http://www.apple.com/server/macosx/">Mac OS X Server</a><br>
Mach<br>
MERT<br>
<a href="http://www.microbsd.net/">MicroBSD</a><br>
Mini Unix<br>
<a href="http://www.minix3.org/">Minix</a><br>
<a href="http://www.minix-vmd.org/">Minix-VMD</a><br>
MIPS OS RISC/os<br>
<a href="http://mirbsd.org/">MirBSD</a><br>
<a href="http://www.mklinux.org/">Mk Linux</a><br>
Monterey<br>
more/BSD<br>
</td><td width="25%">
mt Xinu<br>
<a href="http://www-1.ibm.com/servers/eserver/zseries/zos/support/zos_eos_dates.html">MVS/ESA OpenEdition</a><br>
<a href="http://www.netbsd.org/">NetBSD</a><br>
<a href="http://docs.info.apple.com/article.html?artnum=70038">NeXTSTEP</a><br>
<a href="http://support.nonstop.compaq.com/tools.html">NonStop-UX</a><br>
Open Desktop<br>
<a href="http://www.caldera.com/products/openunix/">Open UNIX</a><br>
<a href="http://www.openbsd.org/">OpenBSD</a><br>
<a href="http://www.opendarwin.org/">OpenDarwin</a><br>
<a href="http://www.sco.com/products/openserver507/">OpenServer</a><br>
<a href="http://www.opensolaris.org/">OpenSolaris</a><br>
<a href="http://docs.info.apple.com/article.html?artnum=72504">OPENSTEP</a><br>
<a href="http://www-1.ibm.com/servers/s390/os390/">OS/390 OpenEdition</a><br>
<a href="http://www-1.ibm.com/servers/s390/os390/">OS/390 Unix</a><br>
OSF/1<br>
<a href="http://www.pcbsd.org/">PC-BSD</a><br>
PC/IX<br>
<a href="http://www.cs.bell-labs.com/plan9dist/">Plan 9</a><br>
<a href="http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?isnumber=3322&amp;arnumber=109264&amp;count=26&amp;index=7">Plurix</a><br>
PWB<br>
PWB/UNIX<br>
<a href="http://www.qnx.com/">QNX</a><br>
QNX RTOS<br>
<a href="http://www.qnx.com/products/ps_neutrino/">QNX/Neutrino</a><br>
QUNIX<br>
ReliantUnix<br>
Rhapsody<br>
RISC iX<br>
RT<br>
SCO UNIX<br>
<a href="http://www.sco.com/products/unixware713/">SCO UnixWare</a><br>
SCO Xenix<br>
SCO Xenix System V/386<br>
Security-Enhanced Linux<br>
Silver OS<br>
Sinix<br>
Sinix ReliantUnix<br>
<a href="http://wwws.sun.com/software/solaris/">Solaris</a><br>
<a href="http://www.bull.com/servers/year2000/spix/">SPIX</a><br>
</td><td width="25%">
<a href="http://wwws.sun.com/software/solaris/">SunOS</a><br>
<a href="http://wwws.trianceware.com/">Triance OS</a><br>
<a href="http://h30097.www3.hp.com/index.html">Tru64 Unix</a><br>
Trusted IRIX/B<br>
Trusted Solaris<br>
Trusted Xenix<br>
TS<br>
<a href="http://portal.acm.org/citation.cfm?id=1041466.1041467">Tunis</a><br>
UCLA Locus<br>
UCLA Secure Unix<br>
Ultrix<br>
Ultrix 32M<br>
Ultrix-11<br>
<a href="http://docs.cray.com/cgi-bin/craydoc.cgi?mode=Show;q=UNICOS%2010.0.1.1;f=books/S-5000-10011/html-S-5000-10011/S-5000-10011-toc.html">Unicos</a><br>
<a href="http://docs.cray.com/cgi-bin/craydoc.cgi?mode=View;id=S-2600-206;idx=books_search;this_sort=;q=;type=books;title=UNICOS/mk%20Release%20Overview">Unicos/mk</a><br>
<a href="http://docs.cray.com/cgi-bin/craydoc.cgi?mode=View;id=S-2336-30;idx=books_search;this_sort=;q=;type=books;title=UNICOS/mp%20Release%20Overview">Unicos/mp</a><br>
Unicox-max<br>
<a href="http://www.unix-systems.org/what_is_unix/history_timeline.html">UNICS</a><br>
<a href="http://www.unisoft.com/history.html">UniSoft UniPlus</a><br>
UNIX 32V<br>
UNIX Interactive<br>
UNIX System III<br>
UNIX System IV<br>
UNIX System V<br>
UNIX System V Release 2<br>
UNIX System V Release 3<br>
UNIX System V Release 4<br>
UNIX System V/286<br>
UNIX System V/386<br>
UNIX Time-Sharing System<br>
UnixWare<br>
UNSW<br>
USG<br>
Venix<br>
Xenix OS<br>
Xinu<br>
xMach<br>
<a href="http://www-1.ibm.com/servers/eserver/zseries/zos/unix/">z/OS Unix System Services</a><br>
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</table>
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Here is now some unixes that are not [yet] in Éric Lévénez's cool history chart:

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<td width="16%">
<a href="http://www.abc80.net/Utstallningen/Luxor/body_luxor.html">ABCenix</a><br>
ACIX<br>
AD<br>
Altos System V<br>
ARIX<br>
AurOS<br>
BOS/X<br>
C Executive<br>
<a href="http://personal.nbnet.nb.ca/mclays/clix.html">CLIX</a><br>
Consensys Unix<br>
Concentrix<br>
ConvexOS<br>
CPIX<br>
<a href="http://www.cromemco.com/EN/HistoryE/historye.html">Cromix</a><br>
CX/UX<br>
DC/OSx<br>
Dell Unix<br>
</td><td width="16%">
DG/UX<br>
DISTRIX<br>
DNIX<br>
DomainOS<br>
DRM System<br>
DTIX<br>
DVIX<br>
ENIX<br>
EP/IX<br>
Esix SVR4<br>
Eurix<br>
FOR:PRO<br>
<a href="http://freemint.de/">FreeMiNT</a><br>
FTX<br>
Genix<br>
HCR<br>
Helios<br>
</td><td width="16%">
HEP-UPX<br>
HI-UX<br>
IDRIS<br>
INOS<br>
LSX<br>
<a href="http://www.lynuxworks.com/rtos/lynxos.php3">LynxOS</a><br>
<a href="http://www.tenon.com/products/machten/">MachTen</a><br>
MacMach<br>
MAXION/OS<br>
MCS<br>
Micronix<br>
Microport SVR4<br>
<a href="http://members.cruzio.com/~bluejay/main.html">MicroPort Unix</a><br>
Mimos<br>
MMOS<br>
MP-RAS UNIX<br>
MST UNIX<br>
</td><td width="16%">
<a href="http://www.lac.inpe.br/~celso/pad/multi.html">Mulplix</a><br>
Munix<br>
NachOS<br>
NCR Unix<br>
NDIX<br>
News-OS<br>
NUXI<br>
Oasis<br>
ONIX<br>
OPUS<br>
<a href="http://www.radisys.com/oem_products/os_software_os9.cfm?MS=Microware%20OS-9">OS 9</a><br>
OS/MP<br>
OSx<br>
PCUNIX<br>
PNX<br>
QNIX<br>
Regulus<br>
</td><td width="16%">
RT/EMT<br>
RTUX<br>
SORIX<br>
<a href="http://en.wikipedia.org/wiki/SOX_Unix">SOX</a><br>
Sphinx<br>
SPP-UX<br>
Stellix<br>
SUNIX<br>
<a href="http://www.nec.co.jp/hpc/sx-e/sx6/software_e.html">Super-UX</a><br>
System B<br>
Thix<br>
TI System V<br>
TNIX<br>
Topix<br>
TOS<br>
<a href="http://www.tropix.nce.ufrj.br">Tropix</a>
<br>
UHC Unix<br>
</td><td width="16%">
Umax<br>
Uniq<br>
Unisis<br>
Unity<br>
UNOS<br>
UTEK<br>
UTS<br>
UTX/32S<br>
UX<br>
UXP/DS<br>
<a href="http://uzix.sourceforge.net/">UZIX</a><br>
VM/IX<br>
VOLVIX<br>
Xoftnix<br>
Zeus<br>
</td>
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</table>
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