This article was first written in February 2006 for the BeezNest technical
website (http://glasnost.beeznest.org/articles/326).
Sun Solaris is probably today's most-used UNIX OS around, probably due to its security  and high-performance approach. It has been traditionally running mostly  on SPARC, a little on Intel platforms, but is now happily running on AMD64  also.
Lately, Sun decided to opensource it, and everybody should probably be  happy of this move. The Open Source version's name is 
OpenSolaris, and various distributions [1]  (or variants) already exist.