UltraStar Deluxe - A free and open source karaoke game inspired by the Singstar™ game, runs on Windows, Linux and macOS.
Clone Hero - Clone Hero is a free rhythm game, which can be played with any 5 or 6 button guitar controller...
Yokee - Karaoke to YouTube videos
Osu - Osu is Music, Rhythm, Single and Multiplayer video game developed by Dean Herbert.
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!
Frets on Fire - Bonus content.