This is the most popular multi-user Operating System in use today. It was originally developed at AT&T Bell Labs. Similar (but not completely compatible) versions have been developed by universities, volunteers, corporations and vendors of high-end computing hardware.

Popular variants, or flavours of Unix in use today include:

  • Solaris, from Sun Microsystems.
  • AIX, from International Business Machines (IBM).
  • Digital Unix, from Compaq (which purchased Digital Equipment).
  • IRIX, from Silicon Graphics (SGI)
  • HPUX, from Hewlett-Packard.
  • SCO, from the Santa Cruz Operation.
  • FreeBSD, maintained by a group of individuals.
  • OpenBSD, maintained by a group of individuals with a single coordinator.
  • NetBSD, maintained by a Foundation incorporated in the state of Delaware.
  • Linux, maintained by a loosely coordinated group of volunteers.

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