Sadly, nothing; not very enthusiastic about programming at the moment. Though I’m currently going through Practical SDR by No Statch Press and learning GNU Radio. It’s basically a flowchart constructor for Python code, so I guess that counts
I used to use a similar piece of proprietary spectral analysis software called SpectraLayers; after switching to Linux, I wanted to move to something open-source. So, I’m just used to that kind of workflow. I mean, Audacity also has an option to display a melodic scale spectrogram, but it’s rather awkward to use, and I don’t believe it ever giving an option to see the pitch of a specific note.
Whereas, Sonic Visualizer lets me do this: 
I occasionally make MIDI covers, so I use Rosegarden for actually transcribing MIDI songs and Sonic Visualizer to figure out the exact notes used in the original tracks. I’ve also messed around with Reaper, FL Studio and various music trackers (SunVox, MilkyTracker etc)
If you play guitar, you might like tuxguitar for doing guitar notation. It does both music sheets and tabs
This is utterly incomprehensible tbh, but I guess I’ll believe it