The green trace is the audio signal waveform, and the red trace is the FFTed version. If you change the CW pitch or the tuning, the peak position moves accordingly.
So this could be a CW tuning indicator in its primitive form.
% gcc -Wall -std=c99 test53.c -o test53 -lm -lasound -lfftw3 `pkg-config --cflags --libs gtk+-2.0`
The library FFTW is used here.