ACM Special Interest Group for Operating Systems
   Tutorial for writing an operating system and links to group members' projects.
   http://www.acm.uiuc.edu/sigops/

Ace Operating System Project
   An open source operating system for X86 architecture. It also contains documents, specifications explaining various hardware.
   http://www.samueldotj.com/Ace/

Agnix
   An open source project, which has been founded to provide an educational, network operating system kernel.
   http://agnix.sourceforge.net/

Bona Fide OS Development
   OS development information and tutorials. Links.
   http://www.osdever.net/

CS 3210 Design of Operating Systems
   A course in operating systems with a focus on the design and construction of a modern OS kernel.
   http://www.cc.gatech.edu/classes/AY2000/cs3210_spring/

Cottontail OS Development Library
   Old non-updated mirror online library covering a plethora of OS development topics. Datasheets, tutorials, reference manuals and hardware programming information.
   http://www.osdever.net/cottontail/

DBLP Bibliography: Operating Systems
   Links to many operating systems journals on the web.
   http://www.informatik.uni-trier.de/~ley/db/os.html

Groovyweb: Operating system programming
   An open source os written in Turbo C (for DOS/ windows) and nasm (Windows/Dos/Linux) as well as two exclusive tutorials on how to write an operating system.
   http://www.groovyweb.uklinux.net/index.php?page_name=Operating%20system%20programming

How to Program a Bootstrap Loader
   A bootstrap tutorial that includes assembly language code to demonstrate loading and executing a binary image from a FAT filesystem.
   http://www.omninerd.com/2005/11/05/articles/40

Intel Pentium 4 Manuals
   The full documentation of system management from Intel for the IA-32 architecture.
   http://www.intel.com/design/Pentium4/documentation.htm#manuals

Inter-Process Communication Tutorial
   Interactive tutorial about message passing, semaphores, and monitors.
   http://cs.gmu.edu/cne/modules/ipc/

KernelCode
   News and reviews of kernels.
   http://www.kernelcode.com/

KernelNewbies.org
   Resources for programmers new to kernel hacking. Example code, FAQs, utilities for debugging modules.
   http://kernelnewbies.org/

Mainframe Programming
   The mainframe continues to grow and transform itself while maintaining its reliability, security and speed.
   http://www.muraleedharan.com/mainframe_programming.html

OSDEV Community
   A web portal dedicated to operating system development, attracting programmers into an advanced development environment.
   http://www.osdcom.info/

OSDev
   OS Development RSS News, forums, and the OSDev Wiki including the largest listing of ameatur operating system projects on the internet.
   http://www.osdev.org

Operating System Lecture Notes
   Notes on operating system theory, source code of describing actual construction of operating system in C programming language. Also OS construction related links to books, notes, tutorials, and news groups.
   http://www.personal.kent.edu/~rmuhamma/OpSystems/os.html

Operating System design & implementation Tutorial
   A educational tutorial on the development of a real mode, single tasking operating system developed in assembler.
   http://www.mohanraj.info/josh.jsp

Pierre's Library
   A resource center for PC operating system developpers. The aim is to provide reliable documents about software and hardware standards under the aspect of official specifications as well as more friendly documents.
   http://perso.orange.fr/pierrelib/

Porting UNIX to the 386
   Historic article series appearing in 1991 that started the open source operating system movement.
   http://porting-unix-to-the-386.jolix.com

Protected Mode and Operating Systems
   Information on writing operating systems, protected mode, and small independent OS projects with freely-available source code.
   http://my.execpc.com/CE/AC/geezer/os/

TAJ Operating System
   TAJ is an object oriented operating system written in C++. It is a multitasking, multithreading and a multiuser operating system.
   http://www.viralpatel.net/taj/home.php

The Basic Kernel Source Code Secrets
   By William Jolitz and Lynne Jolitz (authors of 386BSD OS). Good book to learn the kernel internals of 386 architecture operating systems.
   http://jolitz.telemuse.net/content/books/scs_vol1/item

The OSKit Project
   An open source set of libraries that can be used as building blocks for an operating system for x86. Includes documentation and publications.
   http://www.cs.utah.edu/flux/oskit/

The Operating Systems Resource Center
   Extensive information about booting, file systems, memory, architecture, and interfacing with other devices.
   http://www.nondot.org/sabre/os/articles

Tuomo Kortesmaa
   Notes and example code for basic operating systems concepts, threads, sockets, and device drivers.
   http://users.evtek.fi/~tk/

Virtual Memory Tutorial
   Extensive discussion of virtual memory.
   http://cs.gmu.edu/cne/modules/vm/

Yet Another Object Oriented Operating System
   A project of developing new object oriented operating system.
   http://alzt.tau.ac.il/~michaelg/yaooos/

unixsite.net
   A repository of UNIX-related material, consisiting of: tutorials, programs, source code and miscellaneous information.
   http://unixsite.net/

visopsys OS Development
   A collection of source code, information, and links related to general Operating Systems Development on the Web.
   http://www.visopsys.org/osdev/index.html