PhysTechSoft Ltd. - 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.
RMF-DOS - 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]
Shell Tips - Weblog covering useful tips for a number of command line interfaces including the DOS shell.