DOS

PC DOS 2000: latest version of DOS by IBM
PTS DOS 2000 Pro: latest version of DOS by Paragon, supports large hard drives and FAT32, distributed with source code
DR-DOS 7.03: latest version of DOS by Lineo, fully-functional version available for free
PTS-DOS 2000: latest version of DOS by PhysTechSoft
FreeDOS: DOS distributed under GNU GPL, still in beta stage
Dos Navigator: the best file manager ever made, originally created by RIT Research Labs, open source now
Interesting DOS programs: links to the latest software for DOS
DOS Internet Pages: links to Internet utilities for DOS
CuteMouse: open source mouse driver, supports both serial and PS/2 protocols, uses as little memory as possible
SSHDOS: open source SSH and SCP client for DOS
ChiWriter and user applications: information, additional fonts, printer drivers, and other extensions for ChiWriter
WordPerfect for DOS Updated: information, new printer drivers, patches, and other extensions for DOS versions of WordPerfect
DOS history: DOS is actually older then IBM PC...
Batfiles: the DOS batch file programming handbook
ftp.cyfronet.krakow.pl: polish SimTel mirror - large collection of DOS files

Polish links