Unix

Pronounced 'you-nix' A multi-user, multitasking, portable operating system originally developed by AT&T. 

UNIX is available on a huge range of computational hardware, from a PC to a Cray, and is also available in other, related forms.  For example, AIX runs on IBM workstations; A/UX is a graphical version that runs on powerful Macintosh computers, and Solaris from SunSoft runs on Intel processors.  Many of the computers that make up the Internet run and open source license version called LINUX.