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OpenDOS is a freeware DOS-like and MS-DOS-compatible operating system. It is not "free software" following the definition by the Free Software Foundation, but it is available for private usage including source code at no cost.

It is one name of CP/M-86, which is better known as Digital Research's DR-DOS. Around the time of the development of DR-DOS 6, Digital Research was acquired by Novell, who rebranded the product Novell DOS. The next version was marketed as Novell DOS 7.

The DOS product line was then sold off to a separate company, at that time known as Caldera Systems, owned by former Novell CEO Ray Noorda's investment firm The Canopy Group. Caldera renamed Novell DOS to OpenDOS and initiated a program of source code release, to link OpenDOS to Caldera's other OS, OpenLinux, a distribution of the Linux Unix-like OS.

Caldera released a free version of OpenDOS for non-commercial and evaluation use.

The initial source code released by Caldera was for version 7.01. Only the source code to OpenDOS 7.02 remains available and the company took later development back in-house to produce OpenDOS 7.03. However, this is still available for download at no charge. It is more compatible with real MS-DOS than is the GPL-licensed FreeDOS, for example, and can run Windows 3.1 and Windows for Workgroups 3.11 as well or better than Microsoft's own product. Indeed, Caldera claimed that it had managed to get Windows 95 booting and running on top of OpenDOS in its internal labs, though this was never publicly released.

Subsequently, the DOS and embedded Linux division of Caldera was spun off into a separate company, Lineo. Lineo realised that the old name of DR-DOS still had more market awareness than any of the other names. After OpenDOS version 7.03 was released, the product was briefly renamed to "DR-OpenDOS" (which quickly became pronounced as "droppin' DOS"). Soon after DR-OpenDOS 7.03 was released, the product was given back its former monicker and Lineo released DR-DOS 7.03.

When Lineo was acquired by Metrowerks, the DOS product line was bought out by some of Lineo's former management, who formed a new company, DeviceLogics, to continue its development and marketing - see the article on DR-DOS for more information.

Since 2003 Udo Kuhnt is developing OpenDOS 7.01 again. It has FAT32+ support and several enhancements. It is renamed to Enhanced DR-DOS. The web site is located at [1]

• FreeDOS, a Free/Open Source implementation of DOS operating systems
• CP/M
• MP/M
• DR-DOS
• Multiuser DOS

• Club DR-DOS Wiki
• OpenDOS Stuff
• Unofficial OpenDOS Home Page
• The DR-DOS/OpenDOS Enhancement Project
• Enhanced DR-DOS Forum