Apple Garageband

[Bagpiper]

Since its introduction in 2004, GarageBand has made it easy for novice and experienced musicians alike to perform, record and create their own music. Now, without missing a beat, GarageBand 2 delivers an impressive encore performance, offering, for openers, multi-track recording. That means that you can now play the guitar and sing while recording both tracks at the same time. Or invite the band over to back you and lay down up to eight audio tracks at once. You can accomplish this feat using any audio input/output device compatible with Mac OS X. GarageBand 2 also provides built-in real-time music notation. And it includes smart recording features that let you enhance timing, easily tightening up the rhythm of guitar, bass, vocal, and other real instruments

http://www.apple.com/ilife/garageband/