WaveSpectra is described as 'Tool that (FFT fast Fourier transform) an audio signal as input and sound card, the Wave file, and displays the frequency components (spectrum) in real time' and is an app. There are more than 10 alternatives to WaveSpectra for a variety of platforms, including Windows, Linux, Mac, Android and Flathub apps. The best WaveSpectra alternative is Simple Audio Sweeper, which is both free and Open Source. Other great apps like WaveSpectra are REW, Friture, AUDio MEasurement System and SignalView.