sndpeek - a real-time audio visualization tool (animated, 3D)
Friture - Friture is a program designed to analyze audio input in real-time.
Youlean Loudness Meter - Find your audio's true perceived loudness to prepare for TV and streaming services.
Signalizer - Signalizer is an all-in-one signal visualizing package for VST, VST3 and AudioUnits
Digital Level Meter - Display sound level
dpMeterXT - Precise 10 channel multi-meter supporting all relevant broadcast and streaming standards.