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:

1BSD 2BSD 3BSD 4BSD 4.4BSD Lite 1 4.4BSD Lite 2 386 BSD Acorn RISC iX Acorn RISC Unix AIX AIX PS/2 AIX/370 AIX/6000 AIX/ESA AIX/RT AMiX AOS Lite AOS Reno AppleTV ArchBSD ASV Atari Unix A/UX BOS BRL Unix BSD Net/1 BSD Net/2 BSD/386 BSD/OS CB Unix Chorus Chorus/MiX Coherent CTIX CXOs Darwin Debian GNU/Hurd DEC OSF/1 ACP DesktopBSD

Digital Unix DragonFly BSD Dynix Dynix/ptx ekkoBSD Eunice FireFly BSD FreeBSD FreeDarwin GNU GNU-Darwin Gnuppix GNU/Hurd-L4 HPBSD HP-UX HP-UX BLS IBM AOS IBM IX/370 Interactive 386/ix Interactive IS iPhone OS X iPod OS X IRIS GL2 IRIX Linux Lites LSX Mac OS X Mac OS X Server Mach MERT MicroBSD Mini Unix Minix Minix-VMD MIPS OS RISC/os MirBSD Mk Linux Monterey more/BSD

mt Xinu MVS/ESA OpenEdition NetBSD NeXTSTEP NonStop-UX Open Desktop Open UNIX OpenBSD OpenDarwin OpenServer OpenSolaris OPENSTEP OS/390 OpenEdition OS/390 Unix OSF/1 PC-BSD PC/IX Plan 9 Plurix PWB PWB/UNIX QNX QNX RTOS QNX/Neutrino QUNIX ReliantUnix Rhapsody RISC iX RT SCO UNIX SCO UnixWare SCO Xenix SCO Xenix System V/386 Security-Enhanced Linux Silver OS Sinix Sinix ReliantUnix Solaris SPIX

SunOS Triance OS Tru64 Unix Trusted IRIX/B Trusted Solaris Trusted Xenix TS Tunis UCLA Locus UCLA Secure Unix Ultrix Ultrix 32M Ultrix-11 Unicos Unicos/mk Unicos/mp Unicox-max UNICS UniSoft UniPlus UNIX 32V UNIX Interactive UNIX System III UNIX System IV UNIX System V UNIX System V Release 2 UNIX System V Release 3 UNIX System V Release 4 UNIX System V/286 UNIX System V/386 UNIX Time-Sharing System UnixWare UNSW USG Venix Xenix OS Xinu xMach z/OS Unix System Services

Here is now some unixes that are not [yet] in Éric Lévénez's cool history chart:

ABCenix ACIX AD Altos System V ARIX AurOS BOS/X C Executive CLIX Consensys Unix Concentrix ConvexOS CPIX Cromix CX/UX DC/OSx Dell Unix

DG/UX DISTRIX DNIX DomainOS DRM System DTIX DVIX ENIX EP/IX Esix SVR4 Eurix FOR:PRO FreeMiNT FTX Genix HCR Helios

HEP-UPX HI-UX IDRIS INOS LSX LynxOS MachTen MacMach MAXION/OS MCS Micronix Microport SVR4 MicroPort Unix Mimos MMOS MP-RAS UNIX MST UNIX

Mulplix Munix NachOS NCR Unix NDIX News-OS NUXI Oasis ONIX OPUS OS 9 OS/MP OSx PCUNIX PNX QNIX Regulus

RT/EMT RTUX SORIX SOX Sphinx SPP-UX Stellix SUNIX Super-UX System B Thix TI System V TNIX Topix TOS Tropix UHC Unix

Umax Uniq Unisis Unity UNOS UTEK UTS UTX/32S UX UXP/DS UZIX VM/IX VOLVIX Xoftnix Zeus