open dired item externally

open-externally.el

(defun open-file-externally ()
  "In dired, open the file named on this line."
  (interactive)
  (let* ((file (dired-get-filename nil t)))
    (message "Opening %s..." file)
    (call-process "gnome-open" nil 0 nil file)  ;; switch gnome-open to whatever you prefer. xdg-open is probably sensible
    (message "Opening %s done" file)))

(add-hook 'dired-mode-hook
          (lambda ()
            (define-key dired-mode-map (kbd "<M-return>") 'open-file-externally)))