_(ITS | http://www.its.os.org/) (Incompatible Timesharing System) was a famous *(OS) written by hackers at MIT for the DEC PDP-6 and PDP-10 family during the 1960's and 70's. It was famous for being the antithesis of the _(security)-obsessed CTSS (Compatible Time-Sharing System), by being very hackable and so _(user rights) were a matter of social respect and ethics alone, rather than the dictates of the system, which often limited performance and capacity of the system. ITS was driven by the hacker ethic.

See Also _("A Brief History of Hackerdom - 3. The Early Hackers" | http://www.tuxedo.org/~esr/writings/hacker-history/hacker-history-3.html) by Eric S. Raymond and _("Open Sources Voices from the Open Source Revolution - The GNU Operating System and the Free Software Movement - The First Software-Sharing Community" | http://www.sindominio.net/biblioweb/telematica/open-sources-html/node43.html) by Richard Stallman.