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  (or variants) already exist.