Korn Shell (ksh) is a standard/restricted command and programming language developed by AT&T.
The version from AT&T can be found on AUR (http://aur.archlinux.org/packages.php?ID=13772), but there is also a public domain implementation named "pdksh", which is in extra (http://www.archlinux.org/packages/extra/i686/pdksh/)
Some features are described here: http://bootiack.livejournal.com/294776.html
Making Ksh your default shell
The chsh command can be used to change a user's default shell without root access if the shell is listed in Template:Filename. (If Ksh was installed using pacman, it should already have an entry in Template:Filename).
Grab the full path for Ksh using
$ which ksh
Which will probably output:
Change the default shell for the current user:
$ chsh -s /bin/ksh
Alternative as root, using usermod
Change the default shell for multiple users, using usermod:
# usermod -s /bin/ksh username
After logging back in, verify that Ksh is the default shell with:
$ echo $SHELL