Name: Sonic Visualiser
Homepage: https://sonicvisualiser.org/
Why? No other software in the repos lets you view frequency data of audio over time.
Open source? Yes.
Source: https://code.soundsoftware.ac.uk/attachments/download/2246/sonic-visualiser-3.0.3.tar.gz
As far as I can tell, this project meets the inclusion policy. Lemme know if I missed anything!