xmessage(1) on Linux
The text a5a34e0fac06, as Debian 7 (Wheezy), Debian 6.0 (Squeeze) shipped it.
display a message or query in a window (X-based /bin/echo)
Flags it lists
-
-buttons -
-center -
-default -
-file -
-nearmouse -
-print -
-timeout