Spotify is many things to many people, but one thing it lacks is an equalization feature for letting you adjust bands of bass, midrange, and treble.
Enter Equalify.me, a Spotify plug-in that nestles a 10-band equalizer neatly into the Spotify interface on Windows computers. It's free (donations accepted), and it works, as we know from putting it through its paces on bretberg101's public kraut/spacerock playlist (which, shockingly, lacks both Neu and Faust). In addition to the 10 EQ bands, you get a gain adjuster, which offers another way to control volume, and a toggle control that lets you switch the EQ on or off.
Audio purists generally turn away from this sort of thing, because their $10,000 speakers sound perfect. The rest of us occasionally have the need to compensate for sub-par speakers or headphones, and equalization can come in handy for that--sometimes to add bass, or more often given today's designs, to roll some of those bass frequencies off.
That's about all there is to say about Equalify. If you use Spotify but miss the ability to equalize the sound that's present in other players (like iTunes), the decision to download Equalify for Windows is an easy one to make.