Dunst is a lightweight replacement for the notification-daemons provided by
most desktop environments.
It's very customizable, doesn't depend on any toolkits and therefore fits
in those windowmanager centric setups we all love to customize to perfection.

Configuration:
To customize dunst you have to copy config file from /etc/xdg/dunst to ~/.config/dunst/dunstrc
Then modify it to your liking.