Harmony is based on plugins. Plugins are available for Spotify, SoundCloud, Google Play Music, Hype Machine, YouTube, Reddit, Deezer and local files.
Install various themes and easily switch to a secondary one with Cmd+D. Pre-installed themes: Basic, Dark, Arc & Vibrancy on Mac OS.
All the operations you make on Harmony are mirrored with your services. Like a Spotify track on Harmony, it will be liked on your phone.
Harmony can be controlled using keyboard shortcuts and media keys. Press ? to see the list of available shortcuts.
Whatever size you want it to be, it will follow you
Use the tray or the sound menu integration (Linux) to control the playback even when the app isn't focused. Even more, you can pin the app to the menu bar on Mac OS to access it with ease.
Harmony natively supports Last.fm scrobbling