Catwm is a small, light weight window manager created by pyknite. It was first announced in this (http://bbs.archlinux.org/viewtopic.php?id=100215) forum post.
This requires git.
First, download the PKGBUILD from http://aur.archlinux.org/packages.php?ID=38579. Then, as a non-root user, run:
while in the directory of the saved PKGBUILD. All the files will be retrieved and the package will be built. Then run:
# pacman -U catwm*.pkg.xz
to install the package.