CONV. - Convert YouTube video to MP3, GIF or MP4
Music Pro - Stream YouTube music
Downie - Video download for OS X. Downie supports at this moment over 1,000 different sites.
YouTube Music - YouTube Music is a streaming app primarily designed for Android and iOS mobile devices. The app lets individuals search for music from their favorite artists, enjoy playlists, and access 30 million musical tracks.
Yout - YouTube to Mp3 Converter
YT Music - An unofficial Mac app for YouTube Music