Possibly the thing that has made me happiest this year.
Wordpress, Joomla and Drupal are the main players in the world of web Content Management Sytems (CMS). I have used all three of them.
"Responsive web design (RWD) is a web design approach aimed at crafting sites to provide an optimal viewing experience—easy reading and navigation with a minimum of resizing, panning, and scrolling—across a wide range of devices (from desktop computer monitors to mobile phones).
Mashable called 2013 the Year of Responsive Web Design."