The idea of a multi-user operating system is almost a tautology today but back in the 1980s it wasn't all that common - at least when it came to personal computing. PC-MOS was a multi-user operating system that, like DR-DOS and others, competed with Microsoft's MS-DOS before eventually disappearing at the Redmond juggernaut crushed almost all its competition. Now, Roeland Jansen, Gary Robertson and Rod Roark have put the operating system onto GitHub as an open source project so we can all mess with its source code.