Developed at MIT as a sort of a replacement for CTSS, ITS was a very open system ITS stood for "Incompatable Timesharing System", which was a joke on "Compatible Time-Sharing System", that ran on the IBM 7090 computer. This effort was taken because those involved did not like the direction Multics was taking. ITS is noted for its lack of accounts and security and openness of it's source.
A working version of ITS for either the KA10, KL10, or KS10 can be gotten from here. Running on the KA10 simulator it supports Typ340 graphics displays, TCP/IP via IMP, Chaosnet interface, and many other devices designed at MIT.