notification-thing is a full-featured implementation of the Desktop Notifications Specification. It is not tied to any specific desktop environment, and is focused on features like rate-limiting and flexible filtering to minimize distraction and noise ratio in a transparent way, without silently dropping anything ever.
pulseaudio-mixer-cli is an interactive ncurses UI to control the volume of PulseAudio streams. It is somewhat like alsamixer, but focused not on sink volume levels (which can actually be controlled via alsamixer, with the alsa-pulse plugin), but rather on the volume of individual streams from applications, allowing the user to balance sound levels between them. Interaction with pulseaudio is done through the DBus interface, and the UI is designed to be as simple as possible, without heavy DE dependencies like GNOME libs or KDE/QT.