The Notification Center on Ubuntu 18.04 offers itself well to be used as a todo-list, similar to how I use Notify me on android.
Find a nice icon in /usr/share/icons/gnome/32x32
Test if notify-send works using
notify-send --icon=task-due -u low "hello world"
Add the alias to ~./bashrc
xxxxxxxxxx
# todo command
alias todo='notify-send --icon=task-due -u low '
source ~/.bashrc
From now on, you can use todo hello
to add a "hello" notification in the messaging center at the screen top middle. To view the list, click on the Time Display.