AllMusic
allmusic.com
Browse by genre, mood, decade or who played on it
Sound & Signal
Type one band, get a constellation of adjacent ones
music-map.com
Instant · Works anywhere
Free, no sign-up · online since 2000
Enter an artist and Music-Map returns a cloud of related names positioned by similarity, with the closest matches sitting nearest the centre. The relationships come from what listeners have said belongs together rather than from audio analysis, so the links are often social rather than sonic.
Because the data is decades of human association rather than a model, you get the odd neighbour no audio-similarity engine would ever have proposed.
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Picked for a shared category and overlapping vibe, not for popularity.
allmusic.com
Browse by genre, mood, decade or who played on it
discogs.com
A catalogue of very nearly every record ever pressed
gnoosic.com
Name three bands you like and it guesses the fourth
last.fm
Twenty years of listening data, turned into neighbours
folkways.si.edu
The US national collection of folk and world recordings
whosampled.com
Every sample, cover and remix, traced to its source