Linux kernel development
LinuxMM Linux memory management wiki
[http://linux-mm.org/HugePages Huge pages wiki]
[http://linuxfs.pbwiki.com/ Filesystems wiki]
[http://www.linuxfoundation.org/collaborate/workgroups Linux Foundation Workgroups]
[http://kernel.org kernel.org - Home of the Linux kernel]
[http://kernel.org/doc kernel.org/doc Kernel Documentation]
[http://bugzilla.kernel.org Bugzilla - Linux kernel bug management tool]
[http://crashcourse.ca/introduction-linux-kernel-programming-2nd-edition/introduction-linux-kernel-programming-2nd-edition Linux Kernel Programming Course]
Linux distributions open for participation
[http://centos.org/ CentOS]
[http://www.damnsmalllinux.org/ Damn Small Linux]
[http://www.debian.org/ Debian]
[http://fedoraproject.org/ Fedora Project]
[http://www.gNewSense.org/ gNewSense]
[http://www.linuxfromscratch.org/ Linux From Scratch]
[http://www.opensuse.org/en/ OpenSUSE]
[http://www.pendrivelinux.com/ Pen Drive Linux - Boot and run Linux from a USB flash drive]
[https://www.scientificlinux.org/ Scientific Linux]
[http://www.ubuntu.com/ Ubuntu]
General Linux
[http://tldp.org/ The Linux Documentation Project]
[http://tldp.org/LDP/abs/html/index.html Advanced Bash Scripting Guide]
[http://www.regular-expressions.info/reference.html Regular Expressions Reference - Basic Syntax]
[http://www.grymoire.com/Unix/Sed.html Sed - An Introduction and Tutorial]
[http://www.linuxlinks.com/ Linux Links]
[http://www.linuxcookbook.com/ Linux Cookbook - tips and hints]
[http://www.freesoftwaremagazine.com/ Free Software Magazine]
[http://www.oualline.com/vim-cook.html Vim Cookbook]
[http://thomer.com/vi/vi.html Vi Lovers Home Page]
[http://vimdoc.sourceforge.net/htmldoc/version7.html Vim Documentation]
Security related
[http://www.linuxsecurity.com/ Linux Security] detailed Linux security news site
News sites
[http://lkml.org Linux-kernel mailing list (LKML)]
[http://marc.info/?l=linux-kernel MARC view of LKML]
[http://www.lwn.net Linux Weekly News] - follow the kernel link (changes weekly) (the current kernel page is always http://lwn.net/current/kernel.php3).
[http://www.kerneltrap.org/ Kerneltrap] - news on various free OS kernels (Old, have contacted Jeremy)
[http://web.archive.org/web/20071012002855/http://kerneltraffic.org/ Kernel Traffic (link to Internet Archive)] - a digest of what was discussed on the Linux-kernel mailing list (original site has disappeared)
[http://www.Linux-magazine.com/ Linux Magazine]
[http://www.linux.com/ Linux.com]
Other operating systems actively being developed
[http://netbsd.org/about/ NetBSD]
[http://openbsd.org/ OpenBSD]
[http://www.dragonflybsd.org/ A Peek at the DragonFly Virtual Kernel]
[http://www.freebsd.org/ FreeBSD]
[http://www.minix3.org/ The MINIX 3 Operating System]