This is a free web tool that allows you to remove the vocals from a song to create a karaoke version of it. How good the results will be depends on how the track is recorded. If any instruments are centered, they will also get removed.
The vocals are removed by using the OOPS (Out Of Phase Stereo) effect. The OOPS effect relies on that most songs have the the vocals perfectly centered while the instruments are panned slightly to the left and right channel. The two channels are then subtracted from each other, and since the vocals are as present on the left channel as the right channel, they will cancel each other out and dissapear. Read more about OOPS here .