[dberst]

I'd be happy to see any "songs all in the same key" type playlists if anyone wants to share one

I'm a programmer interested in music visualization and it would be handy to have a few of these

[smitelli]

Not a playlist, but I've always hit up Song Key Finder[1] when trying to figure out what songs might fit together for mashup-type purposes. They rank the songs by popularity within their user community.

[1]: https://www.songkeyfinder.com/

[yaur]

Not a playlist per se, but https://www.hooktheory.com/cheat-sheet/key-popularity

Has popular songs for each key and mode