Ok... Unix can mean a lot of things to a lot of different people. In the late eighties, Sun Microsystems and AT&T teamed up to corner the market on the "future" of the Unix. The result was SVR4 (System V Release 4). There were some implementations outside of Sun (e.g. SCO, Motorola, DG), but Sun is the only popular rendition of it today and it CAN be downloaded:
Solaris Operating System - Get Solaris 10
The other major commercial Unix providers, AIX, HP-UX are based off of SVR2 with their own additions. The other, not so popular, commercial Unix is Tru64 and is yet another variant that was part of an organization called OSF that was designed to counter the Sun + ATT juggernaut. All of that is history... but Tru64 (formerly DEC OSF/1 and later Digital Unix) still lives on. Versions of OSF/1 produced outside of DEC's version are considered collector's items.
Outside of commercial System V altogether is the other branch of Unix called BSD. There are many variants of it out there. The most popular being things like FreeBSD, OpenBSD, NetBSD, Dragonfly BSD... you can google for links to their freely downloadable distros.
Just for completeness, before Sun came up with Solaris (their modified SVR4), they used a BSD variant they called SunOS (1).... technically speaking SunOS always refers to the Sun kernel, but kernels less than version 2 were BSD based and so was the distribution.
Linux is very Unix like... it has most of what Unix has and has many things that are NOT found in commercial Unix. There are some cases where the implementation in Unix is considered better, but the pros for Linux far outweigh the cons.
Most Unix (non Linux) will have limited platform support (well..less than Linux)... so you have been warned. From experience, using Solaris, OpenSolaris and/or a BSD variant from inside of a virtual machine seems to work well and might be a good option if attempting to install directly fails for you.
So IMHO, viable options:
Solaris from Oracle
OpenSolaris (though work has stopped on this)
FreeBSD
OpenBSD
NetBSD
DragonflyBSD
There are some OpenSolaris replacement projects out there... you can google for those (e.g. Illumos, OpenIndiana, etc). Just be warned that NOT all pieces of OpenSolaris were truly open... so sometimes the derivatives might be missing some key pieces.
10-01-2010
