Add Recent Applications to the Dock in OS-X

defaults write com.apple.dock persistent-others -array-add '{ "tile-data" = { "list-type" = 1; }; "tile-type" = "recents-tile"; }'
killall Dock

There are several additional options for that icon when you right click, including Remove from Dock, Recent Documents, Recent Server, Favorite Volumes and Favorite Items.