I went searching for the name of the CMS that About.com uses and I found the answer in CMS Review: Bricolage.
I had never heard of Bricolage before, which surprised me more than a bit.
Right now I'm running sites under WordPress, Drupal, Joomla, and TikiWiki. My search for the perfect CMS has been frustrating and incomplete.
Bricolage may be the next CMS that I try, when I eventually work up the energy to make another attempt at finding the perfect CMS.