Unix Variants & Linux

Debian GNULinux -- The Universal Operating System
LinuxISO.org - A place to learn about, download, and discuss Linux.
Mandrake Linux - Friendly Linux operating system for both servers and desktop
MINIX INFORMATION SHEET
OpenBSD
QNX Realtime operating system (RTOS) software, development tools, and services for embedded applications.
Red Hat -- Linux, Embedded Linux and Open Source Solutions
The FreeBSD Project
The NetBSD Project
Tru64 UNIX publications online documentation
Turbolinux
vector linux
Welcome to SuSE
Wind River - BSDOS 5.0 Internet Server Edition