gxmessage
gxmessage is a GTK based alternative to xmessage
Gxmessage pops up a dialog window, displays a given message or question, then waits for the user's response. That response is returned as the program's exit code.
Because gxmessage is a drop-in alternative to xmessage, gxmessage accepts any option xmessage would, and returns the same exit codes.