UltraStar Deluxe - A free and open source karaoke game inspired by the Singstar™ game, runs on Windows, Linux and macOS.
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!
Yokee - Karaoke to YouTube videos
Karaoke Mugen - Video & Movies and Audio & Music
Sing! Karaoke by Smule - Karaoke with your favorite celebrity singers
KaraokeParty.com - Sing karaoke online and get a score based on your performance.