[alastairp]

For key and BPM data, the MetaBrainz foundation also has AcousticBrainz: https://acousticbrainz.org/ (I'm a developer on this project). Unfortunately, I would say that the data that we have in AcousticBrainz isn't as good as what's in the Spotify API, although the algorithms that we use are completely free (available in the Essentia signal processing library - https://essentia.upf.edu/). Over the last few years the algorithms in Essentia have improved and we're hoping to release a new version of the tool used in AcousticBrainz to improve the database.