Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
Friture - Friture is a program designed to analyze audio input in real-time.
Reaper - Reaper is a focused digital audio workstation (DAW) developed by Cockos. In the creation of the software, the digital audio technology company intended to make audio editing accessible to the masses.
xoscope - Xoscope uses the input of your Sound Card, EsounD and/or a ProbeScope/osziFOX and Bitscope-Hardware.
GarageBand - GarageBand is a fully equipped music creation studio for Mac
Signalizer - Signalizer is an all-in-one signal visualizing package for VST, VST3 and AudioUnits