Install gxmessage by entering the following commands in the terminal:
sudo apt update sudo apt install gxmessage
Description:
xmessage clone based on GTK+
gxmessage provides an easy way to display scriptable pop-up dialogs. Based on the GIMP Toolkit, gxmessage fits in well with desktops such as GNOME, Xfce, and ROX.
Homepage: http://homepages.ihug.co.nz/~trmusson/programs.html#gxmessage
Version: 3.4.3-1
Section: universe/gnome