Emacs greeting appearing in the *scratch* buffer that changes based on the time of the day and day of the week.

greet.el

  ;; Initial scratch buffer greeting
  (defun arun/greet-by-hour ()
    "Greet morning/evening/afternoon based on time of the day"
    (let ((hour (string-to-number (format-time-string "%H"))))
      (cond ((< hour 12) "morning")
            ((< hour 18) "afternoon")
            (t           "evening"))))


  (setq user-full-name "Arun Ravindran")


  (setq-default initial-scratch-message
                (concat ";; Happy hacking " "on a " (format-time-string "%A") " " (arun/greet-by-hour) ", " user-full-name " - Emacs ♥ you!\n\n"))