Linux kernel development
kernelnewbies.org the main kernelnewbies website
KernelWiki (appears to be broken at the moment)
LinuxMM Linux memory management wiki
http://linux-mm.org/HugePages Huge pages wiki
http://linuxfs.pbwiki.com/ Filesystems wiki
Linux-Net Linux networking wiki
DragonFly Status "Changelog" of DragonFly's kernel (appears to be broken)
lkml.org linux-kernel mailing list
kernel.org the home of the Linux kernel
http://linux-news.net linux distro news.
Other operating systems
DragonFly Status "Changelog" of DragonFly's kernel (appears to be broken)
News sites
Linux Weekly News - follow the kernel link (changes weekly) (the current kernel page is always http://lwn.net/current/kernel.php3).
Kerneltrap - news on various free OS kernels
Kernel Traffic - a digest of what was discussed on the Linux-kernel mailing list (no longer maintained)
