This is Microsoft's original PersonalComputer OperatingSystem.
When IBM were about to throw the PersonalComputer into the market, they were looking for an existing OperatingSystem to buy from someone. There is an anecdote that some IBM representants found the Digital Research office closed, whom they were really looking to seal a deal with, so without any serious consideration they also visited this BillGates at his Microsoft company, which back then was tiny. The tactics were already the known ones though - though Gates didn't even have any code, he talked IBM into buying vapourware.
Then he bought some programmer's personal project called QDOS: Quick & Dirty Operating System. The original code had been written by him outside Microsoft in two weeks. Microsoft souped it up it and presented it to IBM as the PC-DOS.
Thus began the victory of hodgepodge crap pushed into the market.
Later, Microsoft tricked IBM to free DOS of its contractual bonds, effectively stealing it back, and marketted their own version under the name MS-DOS.
Nowadays, DOS is obsolete; there are however still applications that depend on it, particularly in embedded devices, so the 
FreeDOS project are working at creating a Free clone.
