I did a little digging, and here's the results. MicroWare OS/9 Level 1 was the first pre-emptive multi-tasking UNIX like OS for a home computer, the Tandy Color Computer 2. It was released in 1983! It did not have a GUI interface though, but that came latter and it was called DeskMate, and you could run OS/9 in less than 64K. The cost was around $50
Last edited by rbelk; 18 December 2006 at 10:32.