ITPRC - Operating Systems

BSD

FreeBSD - Home site for BSD UNIX distributions
OpenBSD Resources - links to guides, tutorials, HOW-TOs and other information sources on a variety of topics

Microsoft Exchange, ISA, .NET

Exchangestuff.com - Lots of Exchange resources
ISAServer.org - Tons of information and resources for Microsoft ISA server
Microsoft Exchange Software - Tools, utilities, and resources for Microsoft Exchange and BackOffice
Slipstick.com - Tons of info on Microsoft Exchange, Outlook and NT Server
Swynk.Com - Microsoft BackOffice Administrators Site - tons of resources including links to various MS related mailing lists

Miscellaneous

BeOS - Information on the BeOS Media Operating System
DriverGuide.com - A collection of various drivers for all sorts of devices
Help Drivers - A huge index of drivers for a variety of operating systems and devices
Magic Cauldron - An informative whie paper on the success of open-source software
OS FAQ - Operating systems news, reviews, tutorials, FAQs, and more
OsOpinion.Com - News, opinions and commentary on operating systems

Novell

SunOS/Solaris

Solaris 2.x FAQ - Frequently Asked Questions for Solaris
Sunfreeware.com - Large collection of Solaris freeware
Sun Guru - Sun Microsystems resource search engine
SunHelp.org - News, information and resources for Sun products
Sun World - Sun Magazine
YASSP - Yet another Solaris Security Package. Freeware for hardening Solaris to attack

UNIX/LINUX

Debian - A freeware Linux distribution
Expect Home Page - Expect is a tool for automating UNIX tasks
FreeBSD - an advanced BSD UNIX operating system for the Intel compatible (x86), DEC Alpha, and PC-98 architectures
Linux Directory - Everything you ever needed for Linus
Linux Documentation Project - Working on developing good, reliable documentation for the Linux operating system
Linux On-Line - News and info on Linux
Linux Today - Ton's of Linux resources inlcuding news, links, lists and more
Linux Virtual Server Project - Details an effort to build Linux-based server clusters
Linux Weekly News - An on-line news-zine focused on Linux
OpenBSD - The OpenBSD project produces a FREE, multi-platform 4.4BSD-based UNIX-like operating system
SAMBA - Provides seamless file sharing between LINUX and SMB/Windows hosts
Unix Resources - Large collection of UNIX resources, by Stokely Consulting
UNIX System Administration Guide - On-line guide to UNIX system administration
UNIX Guru Universe - Ton's of UNIX related stuff

Windows NT/2000/95/98/ME

Bob Cerelli's Windows Page - Lots of tips, tricks and information on Windows
LabMice.net - Large collection of Windows 2000 resources, utilities, and feature guides
Lockergnome - Free newsletters for Windows 95/98/NT and 2000
Microsoft TechNet - Microsoft's resource for product technical information
NT Toolbox - Resources and tools for managing Windows NT systems
RegEdit: The Windows Registry Guide - Comprehensive guide to windows registry files
SearchWin2000 - Portal and search engine for Windows 2000 resources
ServerFiles.com - Tons of nicely organized files for NT/2000/.NET servers
Wayne's Windows 2000 Resources For Administrators and Users - W2K tips, book recommendations, resource links, and more
Win2000Security.com - Provides news, resources, and information on Windows 2000 security issues
Windows-Help-NET - Tips, Tricks and Information on Windows 95/98
Windows 2000/NT Resource Center - large collection of links to Windows information