Wikipedia article covering the history and design of DOS.

Commentary, tutorials, references, Power-Users' Corner, for DOS and related utilities.

Realtime, 32-bit replacement for 16-bit DOS, with modern features: multitasking, demand paging, SMP. Coded in pure Assembly language. Zebor Technology.

In English and German languages; with wiki, downloads, links.

Reduced Memory Footprint; goals: match functions of MS-DOS 6.22, IBM PC DOS 7.00, DR-DOS 7 subset. Written mainly in 2 free C compilers and assembler, most parts are smaller uncompressed than compressed parts of MS, IBM, DR. [Open Source, BSD]

A barebones DOS alternative.

Makes PTS-DOS 2000: network support, file manager, archiver, internal boot virus protection, graphical web browser; email, telnet, FTP clients; many utilities, some for embedded system development.

A free DOS-compatible operating system. Sample applications, discussion forum, and development information.

Weblog covering useful tips for a number of command line interfaces including the DOS shell.