Tictactoe from https://www.youtube.com/watch?v=gk39mp8Vy4M with my slant

tictactoe.el

;; tictactoe.el -- play tic tac toe in emacs

(defun start-tictactoe ()
  "Start playing the game"
  (interactive)
  (switch-to-buffer "ticktacktoe")
  (tictactoe-mode)
  (tictactoe-init)
  (tictactoe-print-board)
  (tictactoe-swap-players))

(defun tictactoe-swap-players ()
  (setq *tictactoe-current-player* (if (char-equal *tictactoe-current-player* ?\X) ?\O ?\X)))

(define-derived-mode tictactoe-mode special-mode "tic-tac-toeeee")

(defun tictactoe-init ()
  "Start a neew game with tititt"
  (setq *tictactoe-board (make-vector (* *tictactoe-size* *tictactoe-size*) ?\.)))

(defvar *tictactoe-board* nil
  "The board itself.")
(defconst *tictactoe-size* 3
  "the size!!!")

(setq *tictactoe-board* (make-vector (* *tictactoe-size* *tictactoe-size*) ?\.))

(defun tictactoe-print-board ()
  (let ((inhibit-read-only t))
    (erase-buffer)
    (dotimes (row *tictactoe-size*)
      (dotimes (column *tictactoe-size*)
	(insert (tictactoe-get-square row column))
	)
      (insert "\n"))))

(defun tictactoe-get-square (row column)
  "Get the row blabla"
  (elt *tictactoe-board* (+ (* row *tictactoe-size*) column)))

(defun tictactoe-set-square (row column value)
  "set the row blabla"
  (aset *tictactoe-board* (+ (* row *tictactoe-size*) column) value))


(defun tictactoe-mark ()
  "mark square"
  (interactive)
  (let ((row (1- (line-number-at-pos)))
	(column (current-column)))
    (tictactoe-set-square row column *tictactoe-current-player*)
    (tictactoe-print-board)
    (tictactoe-swap-players)))

(defvar *tictactoe-current-player* nil
  "current character!")