Still-breathing, major commercial DOSes (not freeware).
MS-DOS is no longer sold by MS. Also, MS has apparently shut down its ftp site, once a source for free v6.22 updates, supplements, etc. Some files are still available online at other ftp sites - try a search for anything you need.
IBM PC DOS 2000 (PC DOS 7.0 with Y2K fix). If you are willing to pay for a DOS, this one is still available and worth considering. Have a look at its feature set, at IBM's PC DOS page. If you already have v7.0, get the free Y2K fix, in 14 languages, at the Y2K Fixpak page.