What are some alternatives?
When comparing AudioTool and Sound Meter, you can also consider the following products
LMMS - Make music with a free, cross-platform tool
Sound Level Meter - You can measure the environmental noise in decibels.
Ardour - Record, edit, and mix on Linux, Mac OS X, and Windows.
Digital Level Meter - Display sound level
Ableton Live - Ableton makes Push and Live, hardware and software for music production, creation and performance. Ableton´s products are made to inspire creative music-making.
GarageBand - GarageBand is a fully equipped music creation studio for Mac