Mac: Spotify is a big program and you don't always want to maximise it every time you want to get a glance at some album artwork or control the music. DockPlayer is a small controller that does that for you.
DockPlayer gives you controls for playback, displays the album artwork, and shows you the progress of the currently playing track. That's all it does, but if you're sick of maximising Spotify every time you want to interact with it, DockPlayer does the job.
DockPlayer ($1.99) [Mac App Store]