What are some alternatives?
When comparing EarTrumpet and Power mixer, you can also consider the following products
Volume2 - Volume2 is an advanced Windows audio mixer, a complete replacement for the standard Volume Control.
Volumouse - From authors website:
Audio Sliders - Volume Control replacement that is five times smaller than its Windows counterpart.
Background Music - Control the audio on your Mac apps from the menu bar
Volti - Volti is an GTK+ application for controlling audio volume from system tray/notification area.
Easy Volume Control - Adjust the sound level on your computer using a customizable keyboard shortcut.