TrackList is a macOS app that acts as a miniplayer for audio players, similar to picture-in-picture. It uses AppleScript to send / receive information from the source. Currently, TrackList supports Spotify. The interface was built using SwiftUI.
I used Kingfisher to load the album artwork in the overlay and handle image caching. Check out the project here.
The icons I used in this app are from JAM that in some cases I modified.