Small program that computes and plots spectrograms, either in a live window or to disk, with support for stdin input. In theory, you can run any data through it and generate a spectrogram. Read the manpage.

In the AUR (but you want specgram-git because specgram has a bug and won't compile!)

RTL-SDR based spectrum analyzer.

CygnusRFI is an easy-to-use open-source Radio Frequency Interference (RFI) analysis tool, based on Python and GNU Radio Companion (GRC) that is conveniently applicable to any ground station/radio telescope working with a GRC-supported software-defined radio (SDR). In addition to data acquisition, CygnusRFI also carries out automated analysis of the recorded data, producing a series of averaged spectra covering a wide range of frequencies of interest. CygnusRFI is built for ground station operators, radio astronomers, amateur radio operators and anyone who wishes to get an idea of how "radio-quiet" their environment is, using inexpensive instruments like SDRs.

The CLI tool is used to set up scanning runs. Data is graphed as output.

Software that takes an image and encodes it as sound. If you look at the spectrogram, you can see the image again. Remember that Aphex Twin album? That. The encoder is Javascript, open the page in your browser. Open result.wav with a spectrogram utility (like Sonic Visualiser) and you can see the image.