xmessage(1) on Linux
The text 8cfa94705bcf, as Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster) shipped it.
display a message or query in a window (X-based /bin/echo)
Flags it lists
-
-buttons -
-center -
-default -
-file -
-nearmouse -
-print -
-timeout