UltraStar Deluxe - A free and open source karaoke game inspired by the Singstar™ game, runs on Windows, Linux and macOS.
Chordify - Chordify turns any music or song (YouTube, Deezer, SoundCloud, MP3) into chords.
Yokee - Karaoke to YouTube videos
muted.io - A magical collection of interactive music theory tools & visual reference pages for musicians and music producers
KaraFun - KaraFun is the best online karaoke. Over 35,000 karaoke songs, with studio quality, at home or on the go. Regular updates. Free demo!
soundrop - Soundrop is an app that allows you to create your own personalized sound track to keep you focused or relax.