Special purpose distributions - usefull tools

I like these useful distributions that have special purpose. I write some down below, do you have any tips about other useful distributions of this kind?

Backup and recovery:

http://www.clonezilla.org/

System rescue:

http://www.sysresccd.org/

Fix Boot:

http://www.supergrubdisk.org/

Firewall:

http://www.ipfire.org/

Network-Attached Storage (NAS):

http://www.freenas.org/

HTPC (more fun than useful maybe):

http://www.geexbox.org

http://xbmc.org