DR-DOS

DR-DOS is a disk operating system for IBM PC compatibles, originally developed by Gary A. Kildall's Digital Research, Inc. and derived from Concurrent PC DOS 6.0, which was an advanced successor of CP/M-86. Upon its introduction in 1988, it was the first DOS that attempted to be compatible with IBM PC DOS and MS-DOS.

Its first release was version 3.31, named so that it would match MS-DOS's then-current version. DR DOS 5.0 was released in 1990 as the first to be sold in retail; it was critically acclaimed and led to DR DOS becoming the main rival to Microsoft's MS-DOS, who quickly responded with its own MS-DOS 5.0 but releasing over a year later. It introduced a graphical user interface layer called ViewMAX. DR DOS 6.0 was released in 1991; then with Novell's acquisition of Digital Research, the following version was named Novell DOS 7.0 in 1994. After another sale, to Caldera, updated versions were released partly open-source under the Caldera moniker, and briefly as OpenDOS. The previously last version for desktops, Caldera DR-DOS 7.03, was released in 1999, after which the software was sold to Embedded Systems by Caldera and then by DeviceLogics. In 2022, DR DOS was acquired by Whitehorn Ltd. Co. and it is now back in development.