DOS
DR-DOS, FAQs, Help, and Tutorials, FreeDOS, Internet, Open Source, Programming, Software, Windows, Doctor DOS Betamax Power-Users' Corner, Dos/Windows commands since v1.00, Georgos the DOS compatible operating system, IBM Corp., Idiots Operating System, Paul Edwards's Programming Page, PC DOS for Embedded Devices, PhysTechSoft Ltd., RealDOS, RMF-DOS
V2 OS
maC's V2_OS stuff, SourceForge: V2_OS TCP/IP stack, Terbium, TheLaser's V2_OS Stuff, V2_OS Project Server
BoxOS
Connects many open source projects together in one neat package; kernel, boot loader, graphical user interface, console user interface, applications, programming languages, drivers, file system support for BeOS, Linux, Windows 95/98/NT. [Open Source, GNU]
Domainatrix
Assembly language OS for Intel/AMD x86 architecture made specifically for serving the Web, written originally for the programmer's personal interest and education after moving to the PC platform from his old 8-bit machine. Philosophically similar to V2 OS.
Download Operating System: LSD
By LadSoft; developed years ago and improved since then; planed for redesign to make a viable OS; updates soon. Extant version is good sample of programming standard PC hardware (no PCI) and managing x86 pmode resources. [Copyrighted Freeware]
FlashOS
Simple OS for x86 CPUs. First designed by Kenneth Garin who still directs and designs project and allows help by others to develop it into a working system. Goal: create whole OS like DOS, with our own ideas of how OS should work: not another clone. [Open Source, GPL]
Hactar
Claims: all new, no equivalent design in extant OSs, an adventure into something really different, an answer to a What if? Runs on 386+, system disk is floppy, kernel size 32Kb; manages 4Gb RAM, 2Gb disk; semi-multitasking; unusual interface. [Open Source, WTOF PL]
HanoiOS
Self booting x86 OS implementation of Towers of Hanoi puzzle, very simple bootstrap loader and kernel; boots, presents shell-like prompt for valid integer input, used by kernel as count of disks to solve, prints list of moves.
PizziOS
One-user, segmented memory OS, written in pure x86 Assembly but may get some C, memory protection via segmentation, FAT-16/32. Main goals: small, fast. Will not be a Unix, but will use block shifting memory management scheme used in some old Unix. Downloads.
Plex86.org
Was FreeMWare. Extensible PC virtualization program to allow running multiple OSs at once on one processor. Runs as much OS and application software natively as possible, the rest emulated by PC virtualization monitor. [Open Source, LGPL]
PM_SZ_OS
Protected mode, 32-bit OS for i486 CPUs and up, full network stack, supports several filesystems, paging, deferred procedure call support, and virtual multiple screens with different resolution and scrollback. Free download.
RDOS
Multi-process/threaded protected mode OS for all i386+ systems, written in all 16-/32-bit Assembly in TASM, fully PROMable so can port to embedded systems with no keyboard and/or screen, stable and secure via segment protection and paging. [Open Source, GPL]
ReWin
Rewriting Windows: new OS now being designed for computers with Intel (or compatible) i386, i.e., with multitasking functions built into the processor. Will be Windows compatible, but won't be a Windows clone: will give Windows executables the needed API so they can run correctly. English/Italiano.
ScottsNewOS
Runs on i386+ compatible, working GUI even on 4 MB. Coded in Assembly, C. Brief description, download link. [Open Source, GPL]
SkyOS
Open-source, full featured graphical (GUI) 32-bit operating system for x86 386+ architecture; network and Sound Blaster support, mice, video, and many file systems. Website shows requirements, screenshots, status, downloads, documentation, contacts, members, forum, mail list.
SuperDOS
Multitasking, multiuser business OS; small (100K), integrated file system, low maintenance. Main purpose: fast business online transaction processing. Usually used in vertical markets such as transportation. Not a (unrelated to) DOS variant. By Bluebird Systems.
Synapse Operating Services
Protected mode, multitasking support, 32-bit; developed on x86-32, intended to run on x86-64 with some changes; DOS-like, but not fully compatible, use: to run ported DOS programs up to 512K. At SourceForge. [Open Source, BSD]
TriangleOS
32-bit multitasking, multithreaded OS for x86 386+ CPUs, with GUI, FSs, applications, drivers, all in active development. Site has information, news, documents, screenshots, downloadable releases.
Visopsys
VISual OPerating SYStem: small, fast, home-brewed, open source OS kernel for x86. Includes project background, screenshots, source code and useful links for OS developers. [Open Source, GPL]
XAOS
Runs on i386+, 16-bit real mode, FAT12/16/32 (read-only, LFN support), coded in C++; downloads: binaries, source, utilities, game (tetris source); downloads. [Open Source]