PC DOS diverged from MS-DOS from version 6, went to version 7, and then around the turn of the millennium had a final commercial release called PC DOS 2000 whic

PC DOS diverged from MS-DOS from version 6, went to version 7, and then around the turn of the millennium had a final commercial release called PC DOS 2000 which was essentially PC DOS 7 with some y2k fixes and other little modernizations. IBM used it embedded in other products until about 2003 after which it's been dead and buried. DR-DOS was bought by Novell when Digital Research went under and became Novell DOS, then it was sold again to Caldera (and later its spun-off Lineo division) where it was called Caldera OpenDOS for a while. It was sold off one last time to DRDOS, Inc. which sold it as a commercial product until at least 2011. I think the current status of the ownership and codebase is unclear.