message-box

message-box is a built-in function in `C source code'.

(message-box FORMAT-STRING &rest ARGS)

Display a message, in a dialog box if possible.
If a dialog box is not available, use the echo area.
The first argument is a format control string, and the rest are data
to be formatted under control of the string. See `format' for details.

If the first argument is nil or the empty string, clear any existing
message; let the minibuffer contents show.