Stuff to check
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Links for websites and stuff you may need for MS-DOS
DOS Batch Script Tutorial, learn DOS Batch and become a senior on this art.
Batch Script Guide & Tricks, be a trickster of Batch scripts and have fun making the computer do what you want: an extension to the above link.
FreeDOS, a good disk operating system with support. It's open source and almost perfectly compatible with MS-DOS.
DOSBox, MS-DOS emulator for most modern operating systems.
Handy programs or sites where to get them
WinWorldPC, a vast library for all sorts of programs for retro operating systems. Windows XP is not included!
mTCP, networking applications for DOS... as long as you have a packet driver installed (see below). There's an IRC client for DOS here!
Crynwr, website with networking packet drivers for DOS
Software Systems, useful DOS programs like a packet driver for 32-bit Windows' DOS emulator (NTVDM)
FreeBASIC, a nice open-source BASIC compiler, way better than QBasic but less compatible with really old video hardware (CGA, EGA, VGA).
Interrupt Jump Table, the whole database of BIOS interrupts, a really good aid for DOS programmers (yes, BIOS exists the whole time while you run DOS)
The dummy page, the core of all the pages in this website and all those created by this stiff. Such lazy fingers! Read its source code if you want to create light and nice pages.