Dowani Online - Produces play-along CDs for classical musicians, with varying speeds and orchestral accompaniment. - http://www.dowani.com
MusAcom - Custom created CDs and Yamaha Disklavier files including diction, accompaniment, and performances of art songs and arias; for singing practice. - http://musacom.com
Music Minus One - All participatory recordings, accompaniment music, play-along and sing-along for all musicians and vocalists, including popular, classical, jazz, rock, and country. - http://www.musicminusone.com