gxmessage is a GTK+3 based xmessage clone trying to be as compatible as possible. You might like it if you're running a mostly GTK desktop. gxmessage opens a window to display a message obtained from the command line, from a file, or from stdin. The window includes a row of buttons, each of which causes the program to exit with a different return code.
WWW: http://homepages.ihug.co.nz/~trmusson/programs.html#gxmessage