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

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/

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/

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

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/

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

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/

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

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

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

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/

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

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

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

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

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

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

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

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

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

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

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

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/

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://pagesperso-orange.fr/pierrelib/

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